There's a Yokomo MR4 Tc Custom in our club. It's been on the top-2 for a good time.
I was close to get one myself, but got another good offer which I choosed, due to my budget
The MR4 is very durable, so parts avaiblity shouldn't be a big problem, but of course, it do matter.
From what I know from the MR4 at our club:
* The CVD's aint the best, so they worn out. Upgraded.
* The shocks are leaking, but they are okay.
* Upgrading the belts helped a lot in acceleration.
So the V-Spec conversion will take you a long way. But remember, using the anti roll bar, requires new A-arms. But the old one will server as spare parts.
I also like to be different, so I'm running a Pro2 (3 months old). It's quite funny to beat the guys with their new fancy cars. So all in all, I would probably upgrade the MR4, if I were you.
But do the math carefully, if your CVD's need to be changed and there's a few parts, which are worn out, it could be too expensive. I know another guy at our club, which got the MR4 Special for a very, very nice price, because of the release of the SD. So if your LHS got one, try and ask him.... This way you also got plenty of spare parts....