Good question Kay. When I was building, I was not going to do the conversion because I was being a weight weenie (they add 3lbs total) then when I told an RV-8 owner/builder (who was already flying) about the option, he said to me I would be crazy not to. He too has since converted and loves it, as he was previously having problems with his aircraft sinking into soft ground, and the 380 gives you a significantly increased contact patch area. I don't have a aviation based reference point to give you as I've only flown with the bigger tires, but here's an example that may put it into context.
Going from a 26" mountain bike to a 27.5 (or 650b for you Euro types) is a 5.7% increase in diameter. Going from a 26" to 29" is a 11.5% increase. The difference in ability to roll over rocks and roots on a 29" bike is massive compared to the 26". The switch from a 5.00x5 to a 380x150-5 is a 8% increase.
From a float perspective on soft ground, the 380 is 23% wider, which combined with the increased diameter, will give a noticeably larger contact patch and subsequent confidence in soft ground. Your tailwheel will sink in before your mains do and I think that's a good order of operations.
It also means you can fit half decient sized chocks behind the wheel and it makes it easier pushing the aircraft on the ground.
In all, yes I would do it again. There are things I wouldn't (like putting in an over priced IFR GPS), but this mod is would have to probably be my #2 favourite, only beaten by the Supertracks canopy opening extension.
Another option to keep in mind if flying off dirt/grass strips is an aftermarket tailwheel. The factory one has a arrestor hook look to it, which won't play well with rabbit holes. I have a JD unit, but there are others out there also that will have a better capability of riding through holes than the factory option.
All said, my next RV will likely be an electric powered RV-9 with 8.5x6 (or bigger) so I can properly land off-field.
Cheers,
Tom.