I purchased a student/teacher license of LR 4 in March 2012 @ Euro 75,- and also have PS CS5 (student/teacher) but don't use PS at all. Looking at the new features in LR 5 I do not see anything that makes me update, not even at academic license prices, so I'll hold-off for now. Depending on whether or not there will be a perpetual license for LR 6 or only the subscription model, and whether or not better alternative products will be available by then, I will decide again a year from now.
So skipping a minor upgrade and using LR 4 for 48+ months means a monthly cost of Euro 1,56 which I deem adequate and acceptable given the functionality of LR 4 and my usage of it. :-)