Having a line-level (RCA) input, or set of inputs, is a good thing if you're going to use a receiver with a subwoofer output. For the ones that I've seen, the "LFE" input has been an RCA input that bypasses the sub's internal crossover, which is perfect when you connect it to a receiver with a subwoofer ouput (because the receiver handles the crossover). If a sub doesn't have an LFE input or crossover-disable switch on it, you can just set the crossover frequency dial to the max and usually be just fine.
So...no, you don't need to make an LFE input a pass/fail criteria when shopping for a sub.
