If you are concerned about mp3 compression, just make your examples a bit smaller, and post at Yousedit, or esnips, whatever, as 16/44 .wav files.
However, the biggest thing most people have to overcome, especially if they don't record themselves a LOT, is the realization that things don't sound the same on playback, compared to how we hear it WHILE WE ARE PLAYING. The mind is an amazing machine, capable of changing your perception of reality, especially when engrossed in a particular task.
It is possible to not notice how buried the drums have become underneath your solo sound, or how drowned in reverb you might have made a registration because you tend to play VERY quietly, or a hundred other things that only playback, through a reasonably accurate speaker will reveal.
Getting used to these things, and learning to compensate for them to achieve a good balanced mix while we play, is the main reason to run tape (or hard drives) a LOT. Especially when working out registrations. Those little iKey or Zoom SD card recorders are perfect for this.
But the other end of this is also the fact that we seldom have our computers hooked up to a decent set of speakers either.... So whatever gets listened to on the web is colored by a usually crappy set of tiny speakers and sometimes a way over-cranked sub!
It's no wonder we never hear ourselves the way we want to...!
An arranger is just a tool. What matters is what you build with it..!