I think Lisa nailed it - it's the "why" that's most important. I'm reading a great book right now called "Soulful Simplicity", and in it, she notes that everything we owns, owns us right back - in terms of money, energy, space, time, etc. So really, I think Lisa's question 'why' is right, and if the answer is not "I love it", or "I need/use it", really think whether it's worth the ongoing cost of it owning you.
Sometimes I think we hold onto stuff for the wrong reasons, but they usually don't make much sense - if it's guilt about money wasted, well, the money was wasted once the purchase was made, we only add to the 'cost' by clinging ... if it's that someone gave it to you, the gift was in the giving, not in the storing ... usually the 'wrong' reasons come down to guilt, and guilt in this case is unproductive, although it can guide us to be smarter in purchasing in the future.
Now, on the other hand, I've often been guilty of over-purging, where I get on a minimalist kick and get rid of a ton of stuff that was perfectly good, flattering, etc. because I was after a particular number, or really pared down palette, only to regret it ... so another practical suggestion is to create a 'holding' area for items you're unsure of, or just sort of bored of but still like ... then this can become a fun 'shop' for you to visit when you need something new and different. You can revisit it after a time (say 6 months later or whatever), pull out what appeals to you, and let go of the rest - it's easier once you've proven to yourself you won't miss it.
Well that was long and navel-gazey!!! Sorry!