Overall, I'd say they're pretty reliable.
Specifically to your question:
The kit costs just a little over $200 (and is a heck of a good deal for all those parts). However, you're looking at minimum 16, usually and most likely 20 hours charged labor to have it installed (at whatever your mechanics prices are?). You can do it yourself as well but it's not for novices. I had a tremendous amount of experience and assistance helping me through it! I would have never attempted it without them.
As to years, there's always lemons. The 04 to mid 08 all had the same common issues. However, not every 04-08 experienced them. Some had 100km problem free. Others didn't make it past 10k. I will say, what I've learned on here is the ignition issues and the second gear issues usually start to present themselves between 10-20k. Can't really speak to the cam issues? Ignition is a wicked easy fix. The others; well, that's what the kit is for.
Having just installed it, I can say...I don't care if I'd had to pay $2k for maintence. My bike would've still been thousands cheaper than any other brand even trying to come close, and still far better than all those said brands!