Distance and Serial or SPI I'm setting up a grid of 200+ slave modules which will be about 12 inches apart and the master will be anywhere from 5 to 10 meters away from the closest module. Each slave module will have a ATtiny85 to manage the sensor reading, LEDs and the network protocol.

The communication packets will be small and will probably be at 115200 baud if using ATTiny85's TTL serial or 1MHz if using SPI. In either case, the modules will be connected in a daisy chain to each other.

Each module will have a resistive touch sensor and be driving about 12 - 16 RGB LEDs (I'm making a step responsive disco dance floor). There will be 12v+ running to each module to drive the LEDs and regulated down to 5V for the ATtiny.

Which brings me to my question. With these constraints, do you think the ATtiny85's built-in serial or SPI would still work well over the 5 to 10 meters from the closest module to the master.

I know some people push towards RS422 or RS485 transceivers for distance applications, but I'd like to keep the total part count down, if possible.
I have a few years working with DMX, SPI (and other serial) &amp; LEDs. I have worked with DMX and a video dance floor for 10+ years previously. I would offer that "some people" are correct. You will get a reliable system with differential pair signalling (such as DMX).
I have found from experience that over 5m of unbalanced serial starts chancing it. Over 10m and you are likely to come up with at least reliability issues, but more likely garbage. 

I have used the TI SN75176B driver a fair bit and is cheap and works. 

Depends on your audience. You can afford to chance it for your bedroom, but not paid business.