Short answer: If you're just playing Wii and Wii U games, probably not worth the upgrade. Everything else, most definitely is. I'd suggest that you switch to it as soon as you're able to as it's much, much better overall.
Longer answer: Aroma comes with a bunch of plugins. From the ones that come included, I personally use Bloopair (for pairother BT controllers), FTPiiU (for FTP access in the background) and SwipSwapMe (for swapping TV and gamepad screens whenever I need one of the other if playing only on gamepad). Nowadays, it comes with the Inkay plugin which enables Pretendo which is a replacement for Nintendo online services. Other than that, I use Padcon (for turning off or putting into sleep the gamepad), re_nfpii (for amiibo emulation), GiveMii YouTube (for enabling YouTube app on Wii U to work once again) and many more. Even RetroArch's Aroma build is getting there, which is really nice, but for now I still use EnvSwap in order to switch between Tiramisu and Aroma because I have Tiramisu build installed on my Wii U.
You don't have to completely remove Haxchi from your system in order to use Aroma, just make sure that you don't use both Haxchi/CBHC and Aroma/Tiramisu at the same time. You'll need to remove CBHC, however, as you'd want to coldboot/autoboot into Aroma instead. Why keep Haxchi? Well, nothing much really, maybe just for the legacy reasons and if you're using some ancient homebrew that didn't get an Aroma port or similar/better implementation.