[ZiggerZagger]

I suppose it matters how much the thrill of the chase appeals to you. In my case, not very much.

My method has been to buy very nice complete sets to begin with, often waiting for quite a while for one to pop up.
Sadly, I have the centering sickness, so I've tended to wait for collector-assembled sets to pop up where it's been clear they've cared about centering and eye-appeal.
From there, I've probably upgraded 10-30% of the cards for perfect centering and condition, depending on the set.
By the time I get to the last few cards, I'm usually getting a bit frustrated, so the thrill of completing things is really more of a relief to me.

It's worked well for me, though, having just completed the last set in my 1953 - 1979 Topps run recently. Took about 6 years or so. Condition is consistent within a given set, and ranges from EXMT to NM/MT depending on year.
I'm sure that buying complete sets to start has cut the final cost of finishing each set dramatically.

I do really enjoy having those sets to leaf through though, and they look amazing when assembled consistently.

I respect and envy folks who are able to just focus on individual examples of cards without feeling the need to be completist about collecting. I would love to get to that state of mind, and feel like I'm getting closer to it as the years go by.