Hm I'm actually using a T420 Thinkpad, and I don't have any problems playing Touhou on this keyboard. I'm guessing that you have an older model, which would explain the keyboard issue.
If you use the computer a lot on a regular basis (I'm guessing you do) and portability isn't an issue, I'd definitely recommend shelling out for a mechanical keyboard. It's a much more comfortable experience compared to a non-mechanical one, and it lasts much, much longer too, so really if you consider longevity, you aren't saving any money by getting a generic keyboard. As long as you're careful to not do things like spill a drink on it (or something similar), then you'll definitely get your money's worth. Besides, keyboard prices are relatively stable, and you aren't going to get a better deal by waiting as with some other computer accessories, so you should probably just get one now.
As for the switches issue, it'd be ideal for you to try out the different switches for yourself and see what you prefer, but if you can't, check out Coreven's link for more details. Really though, it's all a matter of preference, and it's highly likely that if you haven't ever used a mechanical keyboard before, any switch will be fine for you, and that one is likely the one you'll get adjusted to after continued use.
The only real suggestion I have is that if value is a concern, then one of the cheaper and decent mechanical keyboard is the
Razer Black Widow. Free shipping at Newegg too, so it'll only run you $70. It has some reported construction issues, but it's probably one of the better and more popular low cost ones. If you're willing to spend up to $100-130 though, then your options dramatically increase, and at that point it'll be your personal preference, because most good mechanical keyboards are around that price range. Personally, I'd say the extra cost is worth it, but it's up to you and your circumstances.