It's not all or nothing the next few years.
Until the Flyers find that young franchise goalie, they'll only advance deep in the playoffs off a veteran's goalie's hot streak, like Neuvirth against the Nats, a better team could have stole that series behind his play.
Meantime, the team should improve each season the next few years as kids come up and are integrated into the team. The idea they have a window built around Giroux and Voracek is silly, it's not like they've done anything the last five years with those two. The future of the this team is the stream of young players coming up, the old core will provide solid depth and trade bait. The old core will slowly decline but not as fast as the young newcomers improve.
They'll be able to roll three lines and a solid 4th line each season, some names may change but the talent depth should remain. It's far more like that Simmonds and/or Voracek will be traded than a young prospect, both are past their peak age. Over the next three years a half dozen young forwards will join the NHL roster (Rubtsov, Vorobyov, AK, Allison, Bunnyman, MV, Kase, etc) in addition to #2 and Lindblom this year.
Same on defense, with the steady stream of young defensemen, MacDonald and Manning will be pushed out. Eventually Hextall will have to decide who to extend and who to trade, but that's two to three years away.
Meanwhile, the team should improve each season, so I see no urgency to make a trade for a veteran. More likely will be a trade to clear out excess talent (that you'd lose to the cap or roster limits or as UFAs) by trading volume for quality, but that could take many forms, including veterans, prospects and draft picks.