This is my first Mac mini - I bought it along with a 30" Cinema Display but was able to put it to good use as a media server. Since that post, I sold my 13" 2012 MBP. I like the Mac mini better as a media server because I can use it without a keyboard or mouse attached. Mac mini are very underrated. Some 2012 MM models have the same i7 quad core processors as the 2012 15" MacBook Pro models. They can also take two SATA SSDs and the RAM is user replaceable. The 2014 can also take two SSDs (SATA + NVMe PCIe) but the RAM is not user replaceable. I would have bought a second MM if I didn't have the iMac!
The 2012 cMBPs are all still very capable for most tasks. I used to use Aperture and Photoshop on it mostly. I had it connected to the Cinema Display but now I have the iMac connected to the Cinema Display and now have two large screens!
I could see your 2009 MBP becoming long in the tooth for some tasks. Since you have a unused 2011 Mac mini consider getting a monitor like a Cinema Display and using that combination. It would be faster than your 2009 MBP. If you need portability, you can get a 2012 MBP for around $100 these days. If you don't need portability, check out the iMac - the 27" 5k display is amazing! The iMac is not easily upgradeable but it has Thunderbolt and USB 3 ports so fast external drives can be attached. RAM is user upgradeable to 64GB. The CPU can be upgraded but it involves removing the screen.
My current setup,