I am having my house re-wired and and I am considering putting in
dimmer switches for lights and /or ceiling fans.

If you are serious about weak signal DX don't install them.

More tips:
Forget about energy efficient fluorescent lighting.
Wait for LED light bulbs to become cheaper.
LED lights are more efficient and last longer then fluorescent bulbs.
No RFI!

Forget about those new 5.8GHz & 2.4GHz cordless phones.
They generate hash from their computer IC chips.

Use high end RG6 coax and connectors for video distribution.
A quality shield is a must to contain TV hash.
The Belden Brilliance HD digital coax comes to mind - swept to 3GHz!

Use a dedicated ground power outlet for your computer.