Pressure testing is best done with dry nitrogen and a few ounces of R22. The R22 is so a sniffer can find any leaks. But presence of dye is a very reliable sign of a leak, so you might be fine just replacing what you know to be bad, plus the dryer of course. It's not very uncommon for a pressure switch to leak.

You probably noticed that I didn't really answer your question. I think that it's an optional step in your situation. It will cost more up front, but if another leak is found during the test, it will save you money in the end.