I have a couple of licences, one of which is an old lifetime one. tbh I feel i have gotten good value out of it and wil be changing it to a more modern licence type in the near future so I can take advantage of some of the diff features.
tbh if you had bought a copy of MS word 2002 you wouldnt expect MS to give you free versions of word 2010 so I dont see this as being any different. If i want to us ethe new features.. i will update my licence type... in fact i think i wil go do it now :)
tbh it will depend on which apps you have installed and how they install. if they are hooks etc and are listed as compatable with 3.12 then there shouldnt be any issues. I dont know of any skin issues going from 3.11 to 3.12 but it again will depend on which skins they are and what edits, if any, you have made
If you have manually edited any code however then i would guess that you will have to make those edits again.
tbh it will depend on the upgrade. If its a major version change then there are probably going to be issues with incompatability with skins or mods. if its a security fix then less so. However if you have made manual edits to the php files then if they are changed in the new version then you will have to redo those edits
the REALLY easy way to get an upgrade to to raise a support ticket and ask invision to do it for you but to do it yourself isnt a problem - its really very very easy.
ftp the files across and run the upgrade script.. go make a cup of tea and ... your board is upgraded
I would STRONGLY suggest that you perfrom a test upgrade on a seperate install first though to make sure that you will like the "after" version and that everything goes across properly