I started on both bass and guitar 40+ years ago. I tend to favor one or the other for years at a time. I'm actually currrently contemplating playing just guitar for a year or three -- I've really let it slide for the last 5 years or so while I was concentrating on EUB and playing mostly jazz. I've also had a guitar synth for over a decade now, and have dabbled on keyboards since the mid-70s, although I haven't owned one in quite a while. I plan on changing that soon too. I feel that every musician should play keys, really.
I seem to keep seeing the top bassists saying that playing keys is a good thing. So I recently bought an old analog synth (Roland Juno 60). I am having a much easier time understanding music theory than I thought I would with understanding R-3-5. Chords actually make sense. Also the Juno 60 has an arpeggiator and a hold function so I can play a few note and then play bass along with it. This is one of the reasons I went with the Juno 60 over the Juno 106.
The plus on this synth is that there are NO MENUS! Just sliders and switches so I really get to see how patches are made up. This is a study in itself. And man this synth has some seriously thick low end.