Your kenwood does sound like it has some cool features!
You may find, that when you do upgrade to a higher end deck that you may be able to get your recordings to sound even better, doing it by ear.
I found it very convenient and much easier to dub cassettes, once I got a 3 head cassette deck; mine is an aiwa. Having 3 heads enables you to be able to moniter the signal which is being recorded onto the tape while recording, which makes it a lot easier to get exactly the right recording level preferable to you! Hope that makes sense!
I have rarely had bad experiences when using pre-owned cassettes to record, but obviously it does depend on where the tapes have been storred over the past 20 years! I have found that old BASF tapes do tend to have developed sticky shed, meaning that they are really impossible to re-use. But I have never had a problem as far as I remember with 80s mmaxell or tdk tapes.
I agree that the maxell ur tapes that are still available are awful! I've never experienced the particular problem that you had with them, but I have found that after a while, the cassette becomes stiff and won't rewind and forward propperly, and the housing feels very flimsy and not good quality at all! I have found the fe90s to be a little better, but not as good as the tdk d90s and maxell ur90s from the 80s and early 90s.
Everyone seams to have different oppinions about dolby, but personally I don't use it. Mainly just because I actually don't like the sound of it when it's on, and also, if you are going to play your cassette in a different deck, the dolby circuit is likely to be different, meaning that your tape won't sound right. Also, in cheeper machines, I believe that the dolby circuit is of inferior quality.