The JTS I can definitely be without though.
Have you actually driven a post 2003 JTS engined car, or are you just quoting generally perceived wisdom?
The JTS engine did have a lot of coking-up problems in its first incarnation but the later euro4 engine had new camshafts, piston rings, ECU, etc. and is far better (the GTV never had the euro3 engine). There are more problems with the JTS, it is a more advanced & complicated engine than the TS having 4 instead of 2 lambda sensors, direct injection, lean-burn at low revs, higher compression ratio, etc. One of the problems is that the injectors operate in an extreme environment and so really need changing or at least cleaning after about 60,000 miles. I changed mine at 72,000 miles paying £100 each for a set + 4 hours labour to fit, but there was a very noticeable increase in overall performance.
Comparing the 2.0TS to the 2.0JTS, the most noticeable difference is at low revs, the JTS pulls like a tractor, it has massive diesel-like torque when pulling away but no diesel-like almost instantly running out of revs. At higher revs it is practically identical to the TS in performance, but you cannot feel the various stages (inlet manifold length change, valve timing change) coming into action so is less exhilarating.