I dont think the big box store blower has enough power to insulate walls. You need a specific pressure for that - I believe it's 3.7 psi inside the walls.
For the attic, it will work just fine. It makes a big difference indeed - I insulated my attic and recently my basement and it's been great. Last bill of heating was about 30$ including the customer charge. I estimate my highest bill this winter will be around 60-70$ at most. Central PA and high elevation, so it's cold here (6000 average HDD winter). We keep our temperature at 67-68F when home and 60 when going to bed and off when not in the house for long periods of time. So far, with outdoor temperatures in the 20's the house drops during long periods of time to around 60-61F.
We don't have southern exposure unfortunately, so no solar heating gains there. I estimate that if we had, we could go without heat for most part! The house is a 1958 1300 sq ft ranch house with basement.