I have been thinking - on the back of the benefits cap thread, so please forgive if this is not the done thing!
To me, it seems that there is a difference between property speculation - ie buying cheap properties, doing a quick job and selling them on or renting them out at as high a rate as possible in order to rake in the dosh - and DIY?
I'll explain - we are on our 3rd property. Bought a flat cheap, sold it 7 years later for 3 times the purchase price. Bought a house cheap, sold it 8 years later for 3 times the purchase price. (Both times I had a dream that the eventual price we got would be that amount iyswim!) Location - S London - and the times - the 90s - undoubtedly helped in both those cases.
HOWEVER in all three cases, we lived in conditions that I think many would find unacceptable - total rewire, reroofing, replastering, new kitchen/bathroom, damp, no floorboards downstairs in the 2nd house for 3 years, building dust and dirt and debris etc etc. We did all the work ourselves, or knew people who would help out with mates rates when we really couldnt do the work. Both the first 2 properties were finished just a couple of months before we sold. Been in the current house 13 years, brought up 2 DC in 'challenging' conditions - our house now is still a major challenge and years to go before it is what most would call 'acceptable', let alone what estate agents would call 'desirable'.
So we have benefitted along the way from rising property markets - but also from sheer bloody hard work. When we sell this house - should we profit from the effort we have put in, and the market changes as well? if not, why not? and if just from the effort, how would you quantify that? and who would be the arbitrator?