Here's the situation. I feel as though I will not be able to progress on the R1 on the track like I want. It's just too much bike for me. My wife will divorce me if I buy another bike, so I'm forced to either sell my beloved R1, or trade it. There's a guy wiling to trade with some cash for a stock, yet pristine 675. I'm just worried about parts and maintenance.
That does not sound like all that great of a deal unless it's an 09/10 675, and also depending on how much cash.
I picked mine up wrecked in order to build it into a purpose built track whore. I think I paid like $2800 including delivery to my garage from NY to PA. I have at least that much and then some into what you see as the final result in the pictures above.
You can get parts, used parts are often more expensive than say R1 parts. You can score a set of R1 fork for like $300 - good luck finding a set of 675 forks for 2x that. Same for stuff like wheels, etc. There are far less used parts floating around. Just do an eBay search for R1 and 675 and see what you get.
Aftermarket parts cost about the same as they do for Japanese bikes but there are less to choose from. There are plenty race/track bits out there either way for the bike.
Honestly, I think it's hands down the best middle weight made to date. If I were not a quirky and masochistic old fart I'd most likely buy an R6 or a newer gsxr600 and save myself a lot of headaches. But there is just something about the way the 675 runs, turns, feels and even looks that draws me in. I could have done things a lot cheaper with a big 4 I4 600 but then it would not be a 675. If you dump it, it will cost you more to get it back together. It will be harder and more expensive to get parts and it's most likely not quite as reliable as the Japanese supersports but it does not have that "McBike" feel or look. It really is a special bike in many ways (both good and bad).
In the end, it's not the rational choice but in many ways, at least for me, it's the best one.