I have never been able to complete a rainbow collection of any player, I think mainly because the only player that I collect that gets the full treatment is Ken Griffey Jr. and at that point his low numbered cards are going to be well outside of my price range.
I would love to do it because that is a huge accomplishment if you can put together all of the parallels, plates and autographs/relics than that is definitely something to be proud of to have in a collection. But when possible I am happy to help another collector with their goal of putting together a complete rainbow set. The other day I came across a collector who is local who is a 49er fan and was working on a Colin K. rainbow set from the 2013 Bowman release and he needed just the Gold Rainbow parallel #/75 to complete the set. We worked out a deal and he is one happy collector.
I have had some rough days the last few months and there are days where I wonder why I spend money on cards and I get a mental block and have trouble writings posts but when I come across another collector who is excited about finding a card it helps me a bit. It reminds me of the reasons why collecting can be fun.