Need and want are very different things. It depends what you want from your riding. Suspension is a waste of time on-road, it is heavy and unless you lock it out it is wasting energy that should be propelling you forward. You rarely go over 20 mph? I'm not surprised, on a full-suspension MTB.

So, riding a road bike would be a very different experience. Whether it is an experience you want, or would pay money for, only you can tell. I suggest you try a few and see. For me, I'd hate to ride much on the road on a full-suspension 29er. But I'm a bit of an ageing boy racer, and you may not be.