Should I even bother to upgrade from 4.6 to 5.2?

So I have two projects that were developed in 4.6, both of which were 85%-90% complete. I upgraded to Unity 5, and all subsequent versions, and neither game works correctly anymore. I've been spending weeks trying to get them back up to the level they were before. My issues primarily break down to being: - Apparently there was an axis change, since my race game, based upon the car tutorial, now flips all over the place instead of rolling along the track. - Shaders are not acting correctly for me, and a lot of my scene renders as either pink or black. I've gone though and tried to "Fix Now" any materials that weren't right, and changed shaders where I could. - RTP doesn't work the way it's supposed to. New terrains and projects do, but terrains already made are just not working. Tried reimporting it, but it's still not right. So, my question is, do I really need to upgrade my projects to 5.2? Sure I'll develop new projects in there, but these two that begun life as Unity 4 projects are almost done, and don't take advantage of any of the bells and whistles of Unity 5. Is there any compelling reason to continue the uphill struggle of trying to convert them? Tangentially: Can you have both Unity 4.6 and Unity 5.2 installed on the same system without issues?