Question about upgrading my network

[NicolasRage]

Hey guys, until recently I've never used my network for file sharing, just to use the internet.
Due to this I've been happy with my BT Homehub 3, going into a 200mb powerline adapter (no gigabit port), and then up to my non gigabit switch in my office.

The majority of my file sharing will be done within the office, but media streaming will of course be wireless.

Which does it make more sense (budget only permitting bit by bit upgrades) to do;

1. Buy a new 2.4/5ghz N router (no AC devices), run the phone (on ADSL) cable up into the office, and have that in the office, doing away with powerline (for gigabit transfers between the PC's).
2. Buy a new gigabit switch, and just have restricted speed from the router to the switch (my internet speed is only 18/down 1/up anyway).
3. Something completely different.

Any help would be appreciated, I can't spend too much all at once as my other half already wants my head from spending so much upgrading my PC in the last 6 months, haha.
 

Cheers!

[pspfreak]

I would say get a gigabit switch for file transfering and then an wireless access point.