Sound is in the ear of the beholder. There is at least one good example of someone playing a Hilton bass on Youtube (I'm pretty sure he's a TB member and appears to be a very good player) for you to compare to your Warwick/Bootsy example. Just type in "Pete Hilton Bass" in Youtube.
Again, I really like Warwicks; they're my favorite to play and they sound and feel great. I've tried one Infinity that was used for around the $2k mark (I had to pass because it would have been my 5th warwick). It felt and sounded great just like all my others. If you already ordered one, you will be very happy with it. I'm certainly not saying dismiss it. I definitely wouldn't say the Hilton is better either. I'm just saying Warwicks, even Infinities, are a lot easier to find than a one of a kind instrument that Pete would make specifically for you if you're into that. At a quick glance Guitar Center does have the Infinity in stock while there are new and used ones on ebay as low as the $3k mark.
"Frills" seems to be a term used at Carl Thompson's shop (where Pete works) and by his customers to simply describe something that is a little extra to make the bass fancier. You can check out Low End Bass Shop under the "sold basses" tab, then find Carl Thompson basses, and check out the descriptions (or check out Carl Thompson's web site and read some of the descriptions). You'll see what frills means right away. Basically a "no frills" bass will be really basic while a "frills" bass will be much more ornate with more elaborate wood work, stripes, bindings, center blocks, cats eyes, fancy wood selection, etc. Brian at the Low End Bass Shop does have a used Hilton for sale right now for $3999 but it's fretless. I've bought a bass from Brian last year. He's a solid seller and he'd entertain fair offers. He has a couple Warwicks too.