IME, it is something all avid gardeners go through. But space is usually the determining factor, along with increased experience. 25 square feet is not going to accomodate many plants and have them grow happily and successfully. It depends on exacty what you are growing but you should allow a minimum of 1 square foot for most annuals, 2-3 square feet for most perennials and 4-6 for most shrubs. There are obviously exceptions to this but those are good averages to start with. Bulbs generally have very small foot prints initially so those can get tucked in and around other larger, spreading plants.

The best way to avoid compulsive plant shopping is to stay away from any nurseries and plant sales!

I went from a private 1 1/4 acre where I could do whatever I wanted to a very small city lot on a block with very formal lawn and boxwood type yards.

My BACK yard is full of all the plants I love, mostly in pots. The side yard has been turned into my vege garden (the people in the neighboring business don't mind cause they get fresh fruit and veges from me!)

As for the front yard, we have mostly done flowers in pots, added a few iris, done the helstrip in succulents (which I get many compliments!)

We are, this summer planning on converting our lawn and boxwood to Ca native and succulents. Got rid of the boxwood the other day, just deciding what to line the sidewalk with.

It's NOT going to go away, but you will probably have to do more in containers. Look into the container gardening forum, garden junk, small space gardening sites for ideas. Have FUN! ORRRRRRR get a bigger place ;)