Provided it was possible for time to slow down in dreams, I certainly don’t accept that someone could live out a realistic ‘alternate’ life in there. Particularly if they were lucid; things would be forever inconsistent, and there would be no rules. If your friend died, you could bring him/her back by tapping your heels together three times if you really wanted.
It’s difficult to accept that anyone could be unhappy with a dream that lasted the equivalent of several years to their perception. Firstly, you know that while you’re asleep in RL, you’re not missing anything substantial in your life. This is basically FREE time! An additional 10 years in between 2 arbitrary days one year is a bonus - given that you only have 70 to 90 years to live on average before eternal void anyway (depending on your beliefs).
Plus, you wouldn’t be locked into doing anything that you didn’t want to do. If you were, then it’s not really an LD. If it’s not really an LD, then I don’t believe time was actually slowing down, but rather the memories of an extended time period were simply available to you upon waking (as mentioned by Badcandlejack).
There’s also the issue of how your brain can process that much information in only a few minutes real time. Time is all about perception, and to me, this means how fast your brain is going. It might be possible to enhance the speed of your brain, hence slowing down time, but probably not by any significant amount. Maybe you’d get an extra 6 minutes to the hour by increasing your brain speed 10%, but it wouldn’t healthy or easy. Anyway, you can test this now.
I propose time perception is based on the frequency at which your brain is operating. If it slows down, more things will happen between cycles, and it will appear that time is going faster than usual. If you speed it up, less will happen between cycles of observation, and it will seem that time is going slower. Now, increasing the frequency of your brain’s cycles 100 or 1000 times is just preposterous. You’d melt your brain, or something.
(Insert generic disclaimer that the above opinion is based on the physical brain, and not the spiritual mind.)