The Blazers shouldn't operate based on the hope that they snag a premium free agent. Hope isn't a plan and Portland has no proven ability to reel in top free agents. However, it's not a terrible idea to build a good team with some cap flexibility to open up room. While Portland shouldn't be expected to get a top free agent, it's also not an impossibility. A free agent like Marc Gasol deciding on a whim to sign with Portland because he likes the team he'd be joining or the city or whatever else is the kind of lightning that lead to a title.
You shouldn't pass up good opportunities in order to chase that less-likely scenario, but if you can keep that scenario possible while still building a good team, it's worthwhile.