I can see why people find the XC Voyager interiors not it's best - even I remember the interiors from 2001/2002.
The only bit of the interior I find that perhaps could do with a tidy is the bike area on the Voyagers - on route to Leeds, 04/04/19, I caught the 14:13 to Oxford to Birmingham New Street (+ 09:09 on the same journey but on route to Stamford on the 15/06/19) I thought might have been dry blood - I think, however, it was probably more like scratches.
I personally don't think there's anything wrong with the Voyager interiors except for the reduced number of tables. The air-freshener smell has dramatically improved the Voyager experience.
Off topic this next bit but I understand the XC HST interiors have existed since 2008 - I remember, after helping someone lift their pushchair onto the 16:03 at Birmingham New Street (I was heading to Leeds on this on the 04/04/19), entering Coach G where my seat was and the interior smelt clean.
If I'm honest, I think whoever at CrossCountry is in charge of the HST interiors does a great job - XC 170's included!