I just want more of everything, really, but more than anything I'd like more parity. The first DLC was what, 15 cars? All of them were slight variations on pre-existing cars. Then the second car pack contained only four cars, the one after that had 6. With the first DLC there were two tracks, none with the second and one (plus a new mode) with the third.
I'd like it if we got a consistent amount of stuff, i.e. A set number of cars and a track every time. I'd be happy if there were 10 cars per DLC; four or five brand new ones, one or two RMs/TCs and the rest standard > premium upgrades (starting with the AE86!), and as for tracks, anything; remade old tracks, 'standard' tracks (i.e. not as high quality visuals as, say, London) or entirely new ones.
I also think that if you buy the paint pack once, you should automatically get a free one with every subsequent DLC you buy, or maybe one of the sub-sets like the Fluorescents or Gunmetal ones or something, just as a thank you for loyalty I suppose (though the FT-86 II concept and the SPL kart were quite nice).
I don't think additional events is really necessary, but if PD do want to add them they should make them free as they've already been running the seasonal events for quite some time, an additional events pack would just be a group of seasonals all added at once, so it's hard to see the added value in that unless it at least doubles the number of A-Spec events and allows you to run them all in B-Spec too, but just one additional tier would be too little to charge for, in my opinion.
Oh, and I would like to see more tuning options, but that should definitely be free to all players otherwise you could potentially get into a pay to win situation which should remain the sole preserve of the free to play model...
p.s. One thing I want more than anything else is the ability to run one make/manufacturer/country races and make money from them. I don't see why there can't be a procedurally generated mode for this, or the ability to create your own events which lets you specify everything except the payout which is decided by the game. I suppose it would get exploited for easy money somehow, but in the game where people use rubber bands to do their racing for them I don't really see this as a bad thing!
Long, weird post, sorry, I'm extremely tired.