I think if anyone wants to go down the route of using Spring, Play or similar then you MUST spend the time learning it in pretty deep detail. I've seen so many people with "Spring experience" on their CV who can make a webpage appear using the tech but as soon as something goes wrong or they are asked to do something a little different they are screwed as they don't know the framework well enough.
I only use vanilla Servlets and my own stuff because I have been building up my own libraries and ways of doing things over time and I've been burnt enough times with old-school frameworks (like JSF and Seam) that just add so much unnecessary work and ball-ache.
I like to write the fewest lines of code possible and also use the fewest dependencies possible. I find that plain ol' Servlets gives me that for most of the stuff I do.