Looks good as it is mate, wouldnt touch it.
Definite "NO" to 3 door wheels on an S2, they dont go IMO.

My mates got my late spec Saph 15" sharktooths on his S2. Not a common swap but look pretty good.

16's would be a compromise if you dont want to go back to 17's again:
Mondeo Escos style rims or 16" diamond cuts, which aint easy to come by, but do come up on ebay from time to time at decent money.

If it was me, i'd leave it standard or 17" softlines tho.