So I have 3U's of rack space left. What should I purchase?
I already have:
-ART 15 channel EQ
-BBE 362 Sonic Maximizer
-Alesis 3630 Compressor/Gate
-Line 6 POD XT Pro with pedalboard
-Power Conditioner

I was thinking about getting a rack tuner and maybe a 31 Channel EQ, but I don't know what else I should be looking at. Any suggestions?
A dedicated rack delay? Why?

So that when you change presets in your POD, that the sound change is not so abrupt as in from dirty to clean, solo tone to rhythm tone.

How about a power amp?
How about a rack drawer or shelf?

But rack tuner is good.
For an aesthetic option.. find a scrolling text bar, put your bands name on it
Mesa/Boogie Studio Pre | Marshall EL34 50/50 Power | Harley Benton 2x12 V30's

How do you like, your mids in the morning?