I don't have any experience with 303 Protectant but Ultitma Interior Gaurd is a very good product. Very little is needed and have read that some have gotten many months of protection from it. You might need to apply 303 more often, but there are many fans of it here.
I've been using 303 on my car since it was new a little over 3 years ago and a single treatment a year does the trick, along with a few spruce ups with damp mf towel from RW or WW and/or McKee's QID.
In that case, I'd think it needs some conditioning, so I'd go with the 303. UIGP may help some with that also, but I've never used it that way, I've only used it on surfaces in good condition (actually I use Wolfgang Cockpit Trim Sealant--which is pretty similar, I think...unless UIGP has gone water-based).