I seriously doubt clipless pedals make that dramatic of a difference - 20% seems high. I don't routinely pull up on the pedal either unless I'm frantically trying to get up a steep hill, and then I pull up like nobody's business and you really can't beat clipless in that situation.
Anyway, cycling shoes tend to have extremely stiff soles and that makes for a much more comfortable ride in my opinion, power considerations aside. You also don't have to worry about your foot slipping off the pedal and your foot is always in the right spot for you (assuming you got the cleat set correctly)
If you're riding 150km in sneakers you probably don't have the foot issues that I do, but my recommendation to you is to go to a shop with tons of shoes and try a bunch on. You want the shoes snug but not tight and since your feet will likely swell a little on your long rides, you want the ability to adjust the shoe on the go. Different brands fit in different ways obviously.
The other thing to consider is the pedal itself - I've tried a few different systems and some of them really lock your foot in to a given angle, which hurt my knees something fierce. Shimano and Look seem to have fairly popular pedals with a reasonable amount of float and you can go speedplay if you want tons of float. Loads of people use mountain bike cleats because mountain shoes cover the cleat and make walking much more manageable - something you may want to consider for your short jaunts to the store on your bike.