Three years ago I bought my first home, on 1.5 acres. Even though it was basically a blank canvas, I often find myself worrying about it not begin big enough! (And then I look over my shoulder to make sure they're not coming to take me away...yet.)
When I run out of space I will be:
Making sure that there is some kind of garden action going on in every area at all times.
Checking to see if I've maxed out my vertical space! I love vines. They can climb on trellises, trees, shrubs, tuteurs and anything else not in motion.
Starting to look for the perfect piece of roof to start growing a green roof on.
Planting more containers!
And then when I've exhausted all those possibilities I'd most likely start looking to see which garden area I should overhaul completely, and thus start the fun all over again.

LOL!!! I don't have this problem quite yet, but it can't be far away. We bought our house 4 years ago, and calling it a blank slate would be more than generous. It was actually just a big hot mess, 3.5 acres worth! We spent the first year concentrating on fixing the interior (and a veggie garden). Second year was spent having babies (twins). Third year was spent putting in a pool (on top of the old veg garden LOL), patios, stone walls, paths, etc., and I did a lot of foundation plantings. This year is the big gardening year: we're putting in a ~500 square foot vegetable garden and starting to work our way out from the house in terms of other plantings...I think it will probably take me at least another 3 years to actually run out of space, thank goodness!

Oh, what I would do for 1.5 or 3.5 acres! For now I have a city lot that is 60Â x 100Â.
But somedayÂ..

Tilled your front yard?!?! Love it! I have found that my visions of a farm like plot have fallen away. 4 raised beds (16 square feet each) give me plenty for veggies. The flowers and shrubs just sort of go where I want them in a manner that allows for less labor.