I'm very pleased with the look of my car now that it has 65 profile tyres, I don't have any issues with the tyres rubbing on full lock. I don't have any stops on the rack, it's the standard Spyder offering of a LHD Classic Mini rack, I have the control arms drilled to give a smaller turning circle and this means the wheels and tyres really do turn at a sharp angle but no problems with clearance.
Gav, It is possible that the offset on my wheels is different to yours, the wheels on my S4 have a shallower offset than those on my +2, but they will fit the +2 and yes the tyres did rub on full lock when I tried it. Take one of your wheels off and measure to the rear face of the wheel centre ( use a bit of wood or something to span the rim), let me know what the figure is and I will check it against one of mine.
As this exercise is pretty much aesthetic with the added bonus of extra ground clearance it sort of makes sense to use a diameter of wheel that is reasonably close to the original.
The reason Spyder went for the 14 inch rims rather than stick with 13 inch was because there is a far greater choice of performance tyres for wheel diameters of 14 inch and above. Somebody probably made the decision to go with 60 profile for sharper handling and was obviously oblivious to the looks of the car and they didn't weigh more than 60 kilos or have any friends hence they were not bothered with ground clearance either
One of the old regulars on here was building a Spyder Zetec S4 and he was using 15 inch rims with no problems, I can't see any good reason to use 15 inch rims on a +2 other than the aesthetic reasons.
The centre resonator keeps the noise down to bearable levels on longer trips, my +2 has one fitted but still fails the noise test at Castle Combe and records 102db .. (The limit is 100db) but without the resonator it would probably be 104 - 105db -- don't forget that it's a logarithmic scale measurement of noise and that 2 or 3 extra DB equals a lot more noise once you get over 100. Of course beefing up the rear silencer would help here.
Over the last 3 or 4 years myself and others have got Andy and Sean at Spyder to have a look at the more common gripes with the conversion; it almost seemed to me that they just copied what they first did in the late 1990s without a thought towards development, the attitude seemed to be that the conversion worked, so what's the problem.
I'm pleased to say that progress is being made with brake pedal effort and steering lock issues and that my tyre swap has won them over as well.
Sorry for the long blog, hope that answers some questions and gives some more info.