Obviously the amp plays into what kind of speakers you want - so some even goes as far as to buy only powered speakers...
I have Krell pre/power amps driving B&W 802D ($63,000 system) and I found out that I enjoy the brute less sophisticated sound of Onkyo Integra m-306 power amp with Acurus pre (which gives a smooth sound) driving Klipsch speakers - rather forward sounding. The later system costs many many times less, so its possible to build a quite enjoyable sound with mid-fi gears if synergy is well achieved.
My take on the PM's question is it's fun to have many mid-fi systems everywhere in the house, since different systems do different genre music better, rather than just one uber main system...