Yes it will be a different thing that we are going to think if its widely used. We might be keeping more and more instead of just spending it.
Spending bitcoin will make a big impact also for it will circulate from person to person but as who knows how valuable it could be will not be consumers but instead keepers or holders.
People who have invested huge amount in bitcoins will never prefer to spend them as its an investment for them so if they spend then they will miss an opportunity of making profits in future when price goes higher and at this stage they will prefer to simply hold them.
Absolutely. Bitcoin is money. Unless you have megabucks, or multiple streams of income, the Bitcoin will be spent, like money usually is. But, if you can manage to keep your saving in bitcoin, you would generally experience a positive interest rate, over a given year (it really matters what years though; had you caught the slide down from 1000 after Gox, it wouldn't be pretty).