I would like to recommend the underrated Dusk City Outlaws as a game that makes planning a heist fun. Planning a heist in say, Shadowrun can turn into drudgery for exactly the reasons you describe. It doesn't have to, but I think the large number of people saying planning a heist is not fun is strong evidence that it sometimes, or even often, does. Dusk City Outlaws is a game specifically about executing fantasy heists in a sort of Renaissance Italian city-state. It makes planning fun by mechanizing it. PCs get the description of the job, then they have a 15-minute real time scene to make some tentative plans and strategize about what info and gear they'll need for the heist. Each heist has a time limit - "They're moving the stagecoach full of gold in 3 days," etc. - and so they have a limited number of scenes to gather info and set up their schemes. In so doing, they learn concrete, pre-determined info about the target's security measures and what additional complications might lie hidden.
As long as they can come up with plausible solutions to those problems, their plans will generally succeed - but while they're out plotting, they're accumulating Heat, which goes into the GM's pocket as a metacurrency that they can use to introduce plot twists during the execution of the heist and which they'll need to improvise around. The longer you spend during the recon phase, the more you'll know going in - but you'll also have more Heat, which means more possibilities for surprises. Conversely, if you do the bare minimum of legwork, you might have missed some crucial intel, but the GM won't be able to throw as many nasty wrenches your way.
It's designed for one-shots or short campaigns, with a heist being done in no more than two or, for a really complex job, three sessions. The use of some real-time elements is very clever, as it ensures the game moves along at a good clip. That said, you should be careful with introducing it; some people really don't like having to work under time pressure. I found that imposing a 15m limit on planning sessions was the right amount of time - it was enough to ensure that people stayed focused, and I think there might have only been one time where the players felt like it cut them off before they'd covered everything. I actually have taken that as an informal house rule in all my games, whatever the system.