If you are running Yosemite and it's solid what would be the real reason to upgrade to El Capitan?
Doesn't seem like much has changed to make it worthwhile. . Amirite?
That is kinda my problem with OS updates. A lot of third party software breaks. I hate that. For instance, QuickBooks is always problematic. Always a crap shoot whether the current version you are running will work after an upgrade.The only reason you should ever not update is if something is removed that you can not replace with the update.
I have a Mac Mini with 16 gig of ram but I'm still on Mavericks and never upgraded to Yosemite and now here comes El Capitan. I have really enjoyed Mavericks and am afraid to mess up my system with Yosemite and now El Capitan.
Another option is an external drive, this leaves your primary disk untouchedYou can certainly try out 10.11 when it is released on a separate partition on your internal hard drive. It will require an little extra work to setup 10.11. This way your primary partition is left intact and not disturbed.