True: Thunar doesn't do tabs, but can from menu open second window (or more) 2 windows not tabs but doesn't use resources of 2 windows open either) I like it for drag/drop operations.
Sushi and globus are 'file manager' neutral, but I don't think implemented outside gnome yet. Their are some (not nearly as good) file previewers available (Xubuntu uses a couple).
Drop-box integration is available ( the howto is pined near top at Xfce forums) with instructions from Mint-Xfce former maintainer (I think still works on current thunar.
Edit Sorry

Drop box must not be working on current Xfce (link pinned in forum gone now)
I'm not getting how to choose Nautilus over Thunar in LMDE. In Settings->Preferred Applications I can choose Nautilus as my file manager, but whenever I restart LMDE it still launches Thunar,
Must kill Thunar and resave the session setting>startup and session
I can choose Nautilus as my file manager, but whenever I restart LMDE it still launches Thunar
To keep nautilus from trying to overwrite xfdesktop theirs a setting in Gconf under nautilus (never used personally).
and in Nautilus I can't change my desktop background (right click -> Change Desktop Background doesn't do anything).
unless also change/use metacity it doesn't work (unless make a custom action for/in nautilus. Xfce uses xfwm4 & xfdesktop (for now) to manage desktop including background/wallpapers.
J.Jay