I have found a separate, slightly "Kludgey" solution!
When adding new rules to conditional highlighting, it only cuts you off at 15 rules if the rules actually contain text!
What that means is you are able to add many more than 15 rules SO LONG AS YOU DO NOT ADD ANY INFO TO THE RULES UNTIL ALL HAVE BEEN MADE! I will attach a picture with proof.
now as soon as you start adding parameters to your rules it cuts you off, so make sure you have all the rules you need before editing them.
Also I've found that sometimes randomly the rules may not take effect, 1 out of 22 in one of my spreadsheet templates works about 75% of the time...
when that situation arises I use the "table-behind-table" technique described above.
This was driving me crazy as I needed 22 different numbers leading to 3 different colors and "# between X-Y" was not working because of formatting.
it seems to work! And numbers handles the extra rules just fine, I have not tested an upper limit though. would be interesting to see if there is one.
I really hope this helps someone like me in the future. I don't think it's an accepted workflow, but whatever works right?
Notice that "Add a Rule..." is still highlighted as available. Until I add text to any of my rules, I can keep adding more and then edit them all when I'm finished.