RR have been debated in many threads, their figures are often not accurate.
New engines, once run in, have nowdays to deliver what they promised, +-5% as per homologation, but well.
This RR values mean sadly nothing in isolation. Perhaps your engine is a good one and you don't know it, perhaps it is worn or has a sensor prob and you are down on power, who knows...
As of "engine enhencement", I recommend indeed DVA's excellent K13a. That's the best VFM IMHO for a non VVC engine. However, with the kit comes a choice of cams, and in your particular case you can save some money over the regular K13a by keeping your excellent 135 cams and going just the head porting route.
Explanation: in our Elises it makes sense to go for wilder cams than std with K13a, such as 633 (that's the wildest you can reasonably run satifactory on the road) or somewhat more low down torque orientated options. We liked the 633 together with other torque enhencing mods. BUT your car is a 135TF: that comes already with VG cams re power/torque delivery, fitting different torque orientated cams (usual Pipers etc.) would be a waste of money IMHO as very similar to what you already have. And going for wild cams à la 633 is IMHO a mistake in the heavier MG for R & T use, as the MG needs bottom torque, far more than the Elise (unless it is a pure track toy, but then there are other cars for that IMHO).
In short, I would recommend you:
- decide on what you want exactly re power delivery as nothing comes for free
- talk to Dave as he is an excellent bloke who knows all that by heart
- consider going for just a mild head porting (especialy around the valve seats) while keeping the rest as it is. You will see +20hp (with all the goodies you have) at the end over a std 135 while having a very enjoyable R&T car. Oh, and no downside re power delivery, the same of what you have but a bit more everywhere from 2500 to 7200 rpm (with your ECU mod).
Just my 2ps
BTW, that's exactly what we did with our TF135...