Having the same ship just HAPPEN to fall into the hands of another principal character we meet 30 years later is a lot for a viewer to accept. Especially when they're already stretching their suspension of disbelief enough just from R2 & Threepio being linked to both Anakin and Luke through (mostly) chance.

R2 & C3P0 are a given though. Lucas took inspiration from the 2 peasant characters in The Hidden Fortress. They're the lowliest of the low witnessing epic events unfold. It's nice that the audience has these 2 relatable characters to unify the series even if it's far fetched. Their interactions tell us a lot about the universe for starters, and as the most insignificant beings in the universe - just humble servants doing their jobs, it helps to introduce a viewer to this big scary galaxy and its conflict. We relate to them because as spectators, we are 'fish out of water' in this fantastic and unfamiliar setting and in a way so are they (or at least 3P0 is). Adventure is alien to 3P0 and he's being dragged kicking and screaming into one and we're joining him for the ride. The droids' inclusion is forgivable because of what it achieves.

A ship on the other hand just seems superficial.

The fan service in the PT need to be cut down, not added to. Fan service "of a higher caliber" as you say, is still fan service, and all I can see it accomplishing is challenging the viewer's suspension of disbelief. Just my opinion.