Just in my experiments trying to get my own music to sound "best" for free, I've run into so many options: brick wall limiting, 4 & 8 band compression, stereo widening, not to mention getting the EQ just so, etc. etc. etc. If I were trying to produce this stuff for radio, absolutely worth my money to get someone else to do the work. If I were doing this for radio, I'd also hire a guitar player, some studio time to record actual drums, etc. etc. etc.
So, yes it's worth it if that's what you need. Just like it's worth it to buy the brand new F150 with the diesel if you're going to pull a 38' camp trailer with dual slides, but for a truck to haul your trash off, the 80s vintage GMC with a 6 banger will do just nicely...It's about what you're using it for. My mastering is perfectly fine for what I'm doing (writing songs). If someone ever wants to actually use my songs on a project, I'd want them to do it with full tracking and mastering.