Kona guy-
yeah, the old-school CRXs arent' the last word in all-around cars, but for specific jobs they are hard to beat: going fast, handling well. the lightness is the key...nothing touches them, esp. new cars... even new hondas.... all big and porky. Yeah, $10k would easily build either of what I have now, probably with newer/faster parts... or, you could also build a pretty killer turbo miata for about the same $..(maybe a touch more). Whats' up with all these SCCA spec miata guys...$10k to go a little faster than a stock miata...how about $10k and keep the miata part, lose the spec part... (eg. add boost). what kind of SCCA stuff do you do with the Focus? Mostly a road-race guy myself (and instructor for BMWCCA, COMSCC, some other sports car clubs...)
Bikes - yes, those are damn fast...scary too...as said, even a lame bike will crush the fastest of cars.. I had a friend with a whipped 1970's 2-stroke Yamaha R5 that would outrun another friends Talon AWD turbo... at least up through highway speeds...
the ultimate fast wheeled toy I think is karts... 125cc or 250cc shifters...bike-fast but with car-caliber handling and then some. F1 guys use them to 'keep sharp' in the off-season. ;> That says something.
Damn. cars or audio - now that's a tough choice on what to blow money on.