Since you have a Helix, I would say Silverwing, Majesty, or Burgman 400. The Burgman 650 is huge and heavy and awkward, and much more than you need, even on the freeway, unless you plan on carrying a passenger. I would stay with Japanese because of their proven reliability and parts availability, even though a European scooter would appeal to me more.
I won't spend more on a bike than I think it's worth, but if it's a good deal, I don't seem to have a problem buying bikes I don't need.
2002 Vulcan 750, 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
1980 Puch moped