49K on a Valk, not even broke in yet.
49K on a 03 Ultra Classic, ummm?
You can add cruise to your Interstate.
If you park correctly, you won't need reverse. It will mean less desirable parking spots.
You already know the ins & outs of your Valk. Learning curve with the Ultra.
I haven't got close to needing to consider a Trike just yet, but I did help MickManchester convert a Tourer he bought here, triked, then shipped to UK.
I installed the 8 degree tree from Daryl @ vtwinextreme.com, very nice product

Mick had American Trike and Motorsports out of Keene NH install a California Side Car kit.
The kit seemed very nice with fit and trim, but, AT&M were, in my opinion, very lacking to say the least. If you want to have your questions unanswered and be ignored, go there.

So many questions that are of a personal nature when making this choice, but if you convert your Interstate, I'd definitely go Darkside.