Do a search on the net and compare the stats of the NA and the TD, that will give you an idea! I don't think the turbos will be that big so won't be a huge loss in power, but you will notice the difference a fair bit I would have thought.
You are giving the engine less stress so I can't see why there should be any reliability issues. Good idea to check the air fuel mix across the rev range I'd say just to be on the safe side.
I am sure the sump plugs blank the holes off perfectly on the 200TDi which savs you scrabbling around for bolts. But of course I could be imagining that.