I think a top five is doable especially after his Tour ride where he seemed to switch off in the TT and the Tour field was loaded. He podiumed last year and shouldn't deteriorate that much in 12 months or so. His ride at the Worlds was pretty good also. i would be shocked if he didn't finish in the top ten.
I think it would depend on what position the team is in. If Soler or Mas are in contention for the win, I would think the focus would be on working for them. Valverde would then probably ride a similar race to the one he rode at the TDF, which still resulted in a high placing before the TT. I don’t know what shape either are in heading into the race, but Mas will be a podium favorite if his form is good as it was, and Soler’s form was really starting to come on in the last mountain stages and he had planned to peak later for the Giro and not ride the Vuelta. Whatever they decide it should appear to be a much stronger team than it seemed like pre-Tour. Even without a stage win, they proved to be very capable of some results, and Verona has finally come into his own.
Valverde is still able to hang on until the end in the mountains, and Mas has a Top 5 TDF as well as a Vuelta podium (and 2018 wasn’t a weak field by any stretch). Soler finished Top 10 last year. Throw in Verona and you have a team that can do some real damage. It may not be as strong as the Jumbo juggernaut, but I doubt Roglic will be 100% and Dumoulin seems pretty worn out. That leaves Kuss, and he’ll lose 5 minutes in the TT. Carapaz, Landa and Pinot look like the other podium contenders (not rating Froome as a contender). I’m pretty confident one of the Movistar trio can compete with them. I think any of the three could finish on the podium in the right situation. If Mas is on good form, he could compete for the win. I don’t really know what Soler is truly capable of in a GT, Butch he is high placed heading into the TT, he could surprise people. I don’t think Valverde can win the Vuelta anymore, but if they are riding for him, I wouldn’t be shocked if he finished on the podium.
I guess it depends on who is in the best shape. They were all riding much better at the end of the Tour, so it’s hard to say what will happen.