When it comes to track cars I don't think there's much out there that can beat caterhams/westfields & the like. Open cockpit, easy to work on the motor, superlight so no need for huge over complicated engines & plenty of engine/tuning options out there.
Regarding the Celi, no brainer for me. Special car + Rotrex = a car for life! Yes 4wd turbo'd drone cars will beat me all day long but who cares when you're driving something so exclusive. Everybody, young or old loves it, it upsets no one & takes attention away from motors worth 10 times as much. My car will NEVER be up for sale so whatever I spend on it doesn't really matter I'm in it for the long haul now, she gets way more committment from me than my missus does
Bear in mind that with prices coming down so much younger drivers are starting to get their hands on them, which will inevitably result in a lot of gen 7s being totally abused & visually ruined. This baby will be a classic someday, so hold onto it matey!