From what I could tell the complex is connected but i haven't walked between the two yet.
The lobby area of the MGM grand was very nice and if you want a great meal try Juniors. Their portion size are a great deal for the price and the food was really good.
I think the actual casino was smaller then I was expecting especially for the size hotel they built. Their pool is outdoors so that was a drawback for me. But they have an indoor pool at the spa and I am sure they have a day pass you could use. (unless hotel guests can use the spa's pool??)
If your poker players I know I have seen commercials on tv and news casts that Mohegan Sun just opened their new addition of slots, tables, and a Poker room as well, so that might be a trip to think of in the future.
But I liked MGM Grand I think they did a great job with it! The wall behind the check in area was amazing it was a Giant wall of water it was gorgeous.
We don't gamble a lot as we are moving from CT in 3 weeks and need every penny for the move but we got free points from Foxwoods so went there for dinner. Put down 30 dollars on a roullette table and walked away with about 10x that! That was nice!
I'd estimate that the walk would be maybe 10-15 mins if your strolling, less if your walking briskly, and if your running well less then 5 LOL
Hope it helps!