I just got my UniFi two weeks ago and I've almost exactly the same setup. The only different is your RB750 router is my homebrew gentoo box. Seems to work very well but took me the whole week to figure out how to replicate the functionality of the RB750 on my gentoo box. I'm curious though.
Why do you say the above?

--Han.

I think the complication is not your setup but with the VLAN thing TM implement. However, it does seem that many ISP that provide IPTV in other country does the same thing. So maybe it is a standard. Who knows. I've done extensive research into the VLAN, IPTV thing while trying to configure my router and know for sure one of the Australia, ISP implement VLAB for their service. I think the only way for you to make it simple is to have two home plug pair on different ID, then you can remove the RB250SG. But using more home plug network tends to complicate things on another front. It is my opinion that your setup is perfect.

I'm using my old P4 which does contribute quite a bit to my electric bill but well, it is the center piece to my home network and yes it does more then just routing. Besides, it let me do unusual thing like VLAN and bridging. LOL Having full control is a wonderful thing. Also, I did remember you wrote in some other thread that you do need to reboot the RB750 once a week. I can keep my router up indefinitely, especially useful if I go on long business trip and the home network will stay up while I'm gone. Don't want to be getting support calls from wife when I'm working abroad.

BTW, can I ask how come you need to reboot once a week your router?

Humm... OK, I will keep in mind that the RB750G is a viable option for me in the future. Thanks for the info.