what defines progressive music more than anything else are dynamics.
Dynamics and vibes. Building up soundscapes and drifting between different intensities and vibes, which usually increase the lengths of songs dramatically, make alot of songs especially "proggy" in my mind. More so than odd-meter crazy solo sections.
Also, organs. Lots of organs.
Also, songs that change and evolve as they go along are progressive. A prog band doesnt necessarily need to evolve and "progress" as long as the songs they compose do, right?