Thanks very much for your replies,
If I do a search for Coupes up to 5 years old, with a 0-60 of 0-8 seconds I'm getting the following results:
Audi A5 3.0 TDI
Audi TT
BMW 3 Series
BMW 1 Series 120 M
VW Scirocco
Vauxhall Astra GTC
Mazda MX5
However, if I open up the search terms to cars up to 8 years old, I do get more listings for the Audi TT and the Z4 Coupe.
I would rather stretch my budget than go for a car that is as old or nearly as old as my RX8. I guess I'm being snobbish about the registration plate year, but I would like to go for something newer than 2007 if I'm honest.
But, the Audi TTS is a bit out of reach. By the looks of it they go for £14-£15000 on average, which is slightly higher than my budget..but may be possible at a stretch.
The reviews for the BMW 1-Series M aren't great - the biggest complaint seems to be the very hard ride unless you get adaptive suspension. For that reason, I may have to knock that one off the list unless I can be persuaded to give it a shot!
The Vauxhall Astra GTC is a nice looking car and performs well enough for me, but the interior will probably not compare to the likes of the BMW, VW, or Audi and it would be nice to buy something where a bit more effort has been made in the cabin. Might be worth looking at still though.
The biggest bugbear with the VW Scirocco does seem to be the very dated interior, with space also seeming to lack in the cabin when compared with other Coupes; such as the Audi TT. I may still look at these though.
The other models listed (apart from the Mazda MX5 due to the boot space) I'm interested in looking at though.
So I guess I've got a better idea now of what I should be looking at!