I have been on the AE many times - last time was January this year. I agree with MissF - no smell of diesel in the bar - not sure about the sewage smell as we have always gone for a category C cabin and I too can't see the need to upgrade to an A or B cabin.
I did the south trip and on only one island this year there was quite a lot of rubbish [mainly bottles] but as MissF says Captain Fulhu sent the boys over before we set off and they spent the morning clearing the rubbish away.
I was only bitten once [and believe me I am a mozzie magnet!] and that was my own fault as I positioned myself in the undergrowth on one of the desert islands. If you take the usual precautions with repellent particularly on BBQ night you should be fine.
For many years we did the AE and an island for the second week - although my choice now would be 2 weeks on the AE and an island on another occasion - finances permitting!!
I booked very last minute this year - Dec 23rd to fly on January 1 - and went with Marks Travel - they can usually beat the Kuoni quotes. I have never looked at other agents but next time I am considering booking direct and arranging my own flights as many people on board seemed to have done this with no problem at all.