At least in the PMNW hubs, the ramp staff now scan all valet bags that are boarded, so that they're tracked like all the other bags. It's VERY RARE that valet bags don't make the flight. You'd be surprised how many people on a daily basis seem to walk right by the nifty cart in the jetway (the one with everyone elses pick tagged bags) and just randomly put them places. It seems to be practice, at least in MSP and DTW for a ramper to walk up the jettway and look for any straggler bags.
As for cleaning... yes, all the DCI carriers need to improve cleaning, but only so much can be done with very short turn times. Unless you want to take a delay for a clean plane, that is. IMHO there is no excuse for a dirty plane leaving the hub. In an out station where turn times are generally 25-30 minutes there isn't a whole lot of time for a super scrub down. Crossed seatbelts, big garbage pickup, a quick vacuum and a lav restocking and spray is the bare minimum.
As the merger proceeds and DL continues to shuffle the fleet, the CRJ200/EMB145, the worst offenders will be relegated to shorter flights with times less than 2 hours I believe.