Compared to a K-50 a K-3 makes more sense than new lenses unless you want a different FoV. And looking at your two lenses, I'd seriously consider the 18-135 or 16-85. I still use my K-5 even though I use a K-3 most of the time. I'm not convinced that for the average person who's absolute largest print is going to be 30x20, you need anymore than a K-5 for IQ. Yes you can get better IQ with an FF if you buy a the right FF, but, in many cases, you can exceed FF IQ with a K-50. There will be the odd image that an FF does better, but probably not more than 10%-5% of the time. And there are many images on the K-50 that will be equal. A K-3 will give you almost identical IQ to the lower end Full Frame cameras, even in low light. The FF gives you the ability to trade DoF for Noise, at the widest settings. But 90% of the settings available on FF are exactly the same if you match DoF on FF as on APS-c.
SO, unless you're talking more resolution, FF really isn't worth anything very often. You can buy higher res in FF, but, that's really only a factor if you're printing over 30x20 or have a 4k monitor, where you might see a difference with a high res picture, although that isn't confirmed by any actual research that I've seen.
For the most part, the need of FF is hype, not fact. You aren't going to go from not liking your images, to liking your images because you switch to an FF or even a K-3. Your friends who think they are getting better images with their FFs than you can with your K-50 are probably delusional. Most people who think they can get better IQ by buying better gear are. The best guys on the forum get better pictures with their phones than others do with their FFs. The technical specs of the camera are a very small part of that equation.
Work with what you have until you get mages you like. Then think of upgrading. And get a good multi-purpose zoom. You are very limited in your shooting options by the glass you are shooting with.
Last edited by normhead; 09-20-2015 at 08:45 AM.