Yes agreed - Spa.
However Kart Space is really good too.
Haven't used the drivers outfits much but the GT paints are nice if you like decorating your cars. (Tradeable cars painted in those colours can be traded/duplicated but the paints themselves can't)
The cars are good to drive too (especially like the MX5 TC) but I haven't used them extensively yet.
As above - Spa is a brilliant race track - especially from cockpit mode. I could happily drive around there all day, every day. Saying that I hope there are a lot more tracks in the next available DLC packs.