Sometimes, it's clear from the moment we see an all-new car: That one is a great idea. Other times, it's not so clear.

It can take three years or more for an automaker to take an idea from the first sketch to production. Ideas that seemed great at the start can look not so great when the new car finally hits the market.

Or maybe they look great for a while, but not so great after competitors have had a chance to respond. And sometimes, that great-seeming idea really just wasn't so great after all.

We asked three Fool contributors to name the car they feel is most deserving of the designation "no longer made." Here's what they said.

John Rosevear: When General Motors (NYSE:GM) first took the wraps off a concept car called the Cadillac Converj, in 2009, it seemed like a brilliant idea. GM's designers took the underpinnings of the soon-to-be-launched Chevrolet Volt, and wrapped them in a gorgeous, futuristic coupe loaded with top-shelf luxury features.

At the time, there was really no competition for a no-compromises luxury plug-in hybrid with dramatic styling. If GM had rushed it into production and priced it right, it might have been a coup.

Lutz Cadillac Converj Concept Naias

The plug-in Cadillac Converj seemed like a great idea when former GM vice-chairman Bob Lutz first unveiled it in 2009. But by the time it got to market as the ELR in 2014, its moment had passed. Image source: General Motors.

But they didn't. The Volt's development program continued on schedule, but its upscale Cadillac sibling got put on the back burner amid GM's ongoing post-bankruptcy turmoil. After the car's internal champion, former GM vice chairman Bob Lutz, retired, it seemed like the Converj would be left behind, just another show car that maybe could have been something special.

But it wasn't quite left behind. A few years later, when then-CEO Dan Akerson was scrambling around for something to show that GM could compete with Tesla Motors (NASDAQ:TSLA), the program was revived -- and the resulting car, called the Cadillac ELR, finally came to market for the 2014 model year. 

The Converj's design had been changed -- but the ELR was still a great-looking coupe. But it had two huge problems from the start: It was too late, and it was way too expensive.

What had seemed groundbreaking in 2009 -- a plug-in luxury car with 40 miles of electric-only range -- was old hat by 2014, once Tesla's faster, roomier, and more capable Model S had raised the bar. Worse, in what seemed like a classic boneheaded old-GM fit of arrogance, the ELR was priced at an outrageous $75,995.

The ELR's interior is nicer than the Volt's -- although the Volt's is pretty nice. But in terms of range and performance, the two are much the same -- except that you could buy two Volts for the price GM was asking for the ELR. Or a Model S.

GM sold all of 1,310 ELRs in 2014, versus about 19,000 Volts. It cut the price to $65,000 for 2015, and it's offering some minor upgrades for 2016. But meanwhile, the 2016 Volt will be all new and much improved this fall -- and Tesla certainly hasn't stood still in the meantime.

The ELR was never going to be a big seller. If it had rolled out in 2010 or 2011, it might have made a worthwhile brand-boosting impact, and helped to offset the high cost of developing the Volt. By 2014, it was doomed to be an afterthought, at most.

Once that window of opportunity had closed, the ELR never should have been released. But it was, and now it's time for GM to cut its losses and put the handsome-but-outdated little coupe out to pasture.

Travis Hoium: It could be argued that Nissan (NASDAQOTH:NSANY) was the first automaker to make a big commitment to electric vehicles. The Nissan Leaf was the best-selling EV in the U.S. in 2011, when the EV market started to take off -- outselling the Chevy Volt and Tesla Motors Roadster, the only two other EVs to record significant sales.

It even held the top spot for domestic EV sales in 2014, which would probably shock most people. But today, the Leaf is becoming a relic in the EV business, and it's time for Nissan to move on to bigger and better electric options, or get out of the game entirely. 

The problem isn't that the Nissan Leaf is a terrible electric vehicle on its own; it's still a top seller among EVs. The problem is that competitors are flying past it, particularly when it comes to range.

The 2016 Nissan Leaf is expected to come with an 84-mile-range base model, with an option to extend range to 110 miles at top trims. That compares to as much as 270 miles for the Model S, and a more than 200-mile range for Tesla's Model 3 and Chevy's Bolt. The Model 3 and Bolt are expected to be leaders in growing the mass adoption of EVs. Once a cost-effective EV with 200 miles in range is available, why would consumers buy one that gets half that? 

If Nissan wants to compete with the likes of Tesla Motors, GM, or BMW -- which are all making big bets on EVs -- it will have to step up its game, and improve both range and the appeal of its products. If it doesn't, the company will quickly go from a leader in the EV revolution to a company playing from behind.

Rich Smith: In four years, Tesla Motors plans to relaunch the Roadster sportscar, the niche electric vehicle that "started it all." This, however, is an idea that deserves to get the ax before it grows into so much as a sapling.

I mean, seriously, why does Tesla think it needs a new sports car? 

Tesla's "plain vanilla" sedan is the Model S. In its basic configuration, the Model S is already faster than most sports cars made by other manufacturers. And Tesla recently announced an update to the P85D Model S variant that enables the car to accelerate from zero to 60 mph in 2.8 seconds.

Two. Point. Eight. Seconds. 

That's nearly a full second faster than the fastest BMW. But Tesla thinks it's not fast enough? It thinks there's a market for a Roadster sports car that rockets to 60 mph faster than you can count one-two-three? What's next -- push-button warp drive?

Honestly, I think Tesla is making a mistake in sinking money into developing a new sports car. The Model S isn't just fast enough; it's wicked fast already. More important, it's selling in volume, and volume is what Tesla needs to do if it's to ever stop burning cash, and start earning profits. 

Tesla says it wants to have 1 million Tesla-brand cars on the road by 2020. It's aiming to sell 55,000 this year, and perhaps as many as 500,000 per year by 2020. In contrast, the company only ever sold about 2,500 Roadsters -- and that was back when there was no Model S, Model X, or Model 3 to buy as an alternative. 

If volume is the key to Tesla's success -- and it is -- then Elon Musk needs to keep his eyes on the road, stay in the mass-market lane, and not let his head be turned by a sexy new Roadster.

John Rosevear owns shares of General Motors. Rich Smith has no position in any stocks mentioned. Travis Hoium has no position in any stocks mentioned. The Motley Fool recommends General Motors and Tesla Motors. The Motley Fool owns shares of Tesla Motors. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.