I cancelled my pre-order deposit for my '19 TRD Pro as well and switched it to the 2020. The army green color was what I really wanted and I was looking at upgrading the head unit down the road any way. Now that it has CarPlay/Android auto, I won't have to do that.
Like you, I also bought quite a few accessories/mods (black chrome exhaust tip, Blue TFT Accessory Meter Display, Salex organizers, TRD oil cap), but that didn't stop me from switching. I don't know if the exhaust tip and the Accessory Meter Display will fit/work on the 2020. If it doesn't, I'll just sell it to recoup most of my costs.
The way I look at it, is that I keep my vehicles for longer than the average person. My daily driver is a 2006 Sienna, which I can't wait to get rid of. lol. We've had it since 2009 and my family no longer needs a 3 row minivan. If I would've kept the preorder on my 2019 TRD Pro, which I would've got at the end of this month or early/March; then I'd be kicking myself for the next 10 years every time I see an Army Green 4runner.
Do what you think is best for you. Like others said, there will probably be even better deals on 2019 4Runners once people start holding off for the 2020's.