Truthfully, for most living rooms, 50-80 watts per channel is plenty. But you can get more power from separate amps. I'm not so convinced of superiority of separate power amp and preamp over a good integrated amp.
The tuner section... there are few receivers that have tuner sections as good as a medium priced tuner. And if you want really good FM performance a separate tuner is almost a necessity.
For example, I have an Onkyo Integra TX-870, and while a good tuner section, (3-filter), it is easy to find Onkyo tuners with 4-filter/5-gangs, such as the T-4017, T-4087, T-4500. Or even more sophisticated tuners such as the T-4700, T-9090 II.
In my main system, I have an Onkyo P-3200 preamp, M-5150 power amp (150 w/ch), and T-4500 tuner (with filter mods). My bedroom system has an Onkyo TX-866 receiver, 80 w/ch. But I have also added a third stage of filtering to the 2-filter tuner by placing components back in the empty spots on the circuit board, following the European version schematic.
To me, receiver vs. separates depends on how much importance you place on FM reception.