It really depends on what you want to spend I suppose. I have a 2006 NC1 and started off on 16 inch wheels and the standard (not Bilstein) suspension. Handling was ‘ok’. I fitted yellow dot ARB’s front and back and the reduction in body roll was substantial. Next I fitted a low mileage set of Bilsteins and springs from a later NC3.75 Sport. Handling was much improved, then added 17inch alloys and new tyres. Cost of the suspension changes was just over £200 and I did the geometry setup myself. It’s been like this for a few years now and have no inclination to change it. I do a lot of fast road work and the occasional track day and this set up is more than adequate IMO with the mighty 125bhp I have 
. I didn’t go for lowering springs for the sake of ride comfort but the later shocks did drop the front ride height by ~10mm. Handling on the limit is very composed when driven hard and with a standard 1.8 or 2.0 you don’t really need to do more, unless you want to of course. You also mentioned the front ride height on yours. If it’s as high as you indicate, check the bottom wishbone bushes aren’t the problem (loads of posts on here about that). Hope that helps in your deliberations.
Thanks Matt for you’re extensive reply, it is for sure a tricky subject, I suppose the earlier models were designed to mimic the classic feel of a British sports car, unless mine is broken somewhere 
, or unless like somebody mentioned on here I’m expecting too much, coming from an S2000 and an RX8.
I suppose I’m just chasing that more stable feel on the limit, something you seem to have captured using the later model bilstein suspension, and RX8 ARBs.
Maybe this is the best setup for me also, but I will check the front bushes too 
I also, see PuffyPinkPanda’s, had Meister coilovers fitted at Cleverley’s now Vincent Motor Works at Stradbroke, just down the A140 from Norwich. I’d pop in there and see what Vincent recommends. There’s the matter of wheel alignment which I don’t think has been mentioned which VMW carries out. It’s worth going and having a chat.
Ah that’s not far from me at all, I’ll pop in and see what they recommend. Thanks for that
I’ve checked the front bushes and they are fine, I also compared my front ride height to others on Auto trader and it seems to be the norm for earlier cars.
I’ve already had geo and new tyres all round, so I’m guessing more roll is due to increased ride height on the earlier cars which would make sense as later cars seem to be using the bilstein setup with lower suspension.