When you are adding on to your exhaust remember that nothing is free. What I mean by this is that when you add on to the exhaust you are creating more pressure inside of the exhaust system. This increased pressure will cause a loss in power of the engine. How much loss? That's hard to tell, it could be so small that you may not notice or it could be quite a lot of power lost. All I can say is to try it and then see how the plane performs. If it's still acceptable power levels to you then keep the exhaust extension. If not, remove it.

IMHO I don't mind cleaning the plane at the end of the day. I just consider it part of the hobby. In fact, cleaning your plane should be an important part of your maintenance routine at the end of the day. As you clean make it your habit to start checking the condition of your plane. Holes in the covering, hinges secure and tight, clevises tight and secure, wheel collars tight, cowl and canopy screws tight, all hatches tight, etc...... The hands on time you take cleaning your plane could well save the plane by noticing anything that is wrong and correcting it before you fly. I've seen pilots do a quick wipe down and not check anything thing on their planes. In fact, we have a guy that seems to ALWAYS be crashing a plane at the field. The reason why he is always crashing is because he never does any preventative maintenance and check for things like this. He wipes down the plane and throws it in his car. He won't check anything and then pull it out next time and fly it. This lack of checking is what causes his crashes. Sorry for getting so off track here, but I'm just trying to point out that the time you spend cleaning your plane can be more productive to you than just cleaning the plane. It can help you find problems that could lead to a crash.

Hope this helps

Ken