Eventually you'll wear the tread off the current tyres and have a perfect road tyre!

You're limited to the 26 but not the 2.1. I use some cheap-and-nasty 26x1.9 slicks that nonetheless work fine. I prefer fatter tyres as you can run them at a lower pressure, which makes for a smoother ride on anything other than a perfect flat road (does such a thing really exist) You don't need any kind of tread pattern for riding on paved roads (bicycle tyres don't hydroplane) but most will have a light tread pattern of some sort which is mainly cosmetic.

I also have a set of schwalbe land cruisers which are a good combination tyre, which are useful if you ride a mixture of on/off road surfaces or in patchy snow. The idea is that the smoother central section contacts the road on hard surfaces, with the side tread coming into play on softer stuff or at a lower pressure.