The way the Solo rules are written, having "the" car will always be an issue... You can certainly have fun and maybe even win once in awhile with an "outside" car, but unless they start adding weight to certain models and having weight and class checking at tech for each event (both unrealistic), it just is what it is.
I've run three different cars this year (my first). A '78 Spit 6 in SSM, an '03 TDI wagon in HS and an '07 MINI Cooper 'vert in HS. I've always had fun (although the Spit was a trying experience), but my best times in class were with the MINI (and I'm not running R-comps... yet).
We have enough national-caliber drivers in our region to be able to gauge my progress against their times. If I get to a point where I feel like the car is really holding me back, then maybe I'll worry about having the "it" car... Somehow, I doubt that will happen for some time... if ever... I spent enough time losing at DH racing to ever worry much about winning in auto-x.
One nice thing about running in stock classes is the limited mods can actually be a relief if you're on a limited budget: "Nope... can't do that mod as it would put me in a bad PAX." To this end, I plan to put some Koni Yellow's on the MINI in addition to the r-comps, but that's about it.
Then I either start saving up for a F500/F-Mod car... and/or I build my old Volvo into a SM car...