From what unseeing, not much unless they are lifetimed. If so, they may be worth the lifetime fee you paid.
I have three of them that I can't bring myself to list on eBay and ship. They aren't even fetching the value of the 2tb drive inside them.
I also have an XL4 in the same situation - looks line it MIGHT get $100 - eBay fees.
I was hoping to get super cheap lifetime on them when I swapped them out for Roamios and minis, but no dice.
Tivo Roamio Pro,
Tivo Premiere Elite
3 x Tivo Mini
Samsung 72" HL72A650 DLP HDTV
Samsung 56" HLP5674 DLP HDTV
Sony 40" LCD HDTV
iRule + iTach Remotes