There are lots of ways to step up your brewery, as reflected in all the comments.
For myself, after taking small steps with my MB kits (adding adjuncts and steeping grains), I moved to making original recipes with DME/steeping grains and hops. Then I made a big leap and bought a 5-gallon starter kit online and my brother built an 8-foot long fermenting/bottling station in my basement.
I decided to go all-grain and built a mash tun similar to BlackDuck's.
I recently started kegging.
These may not be options for you, but it's the path that worked for me. I like the creativity of coming up with my own recipes. I like the challenge of researching a style and brewing according to style. I like having a lot of variety in my pipeline, so in addition to the 5-gallon batches, I also make 2.5 gallon batches. Sometimes I prefer an easier brew day, so I've formulated recipes using just extract and steeping grains, rather than doing AG all the time.
I guess maybe what I'm getting at is that it's not the process that matters so much as how you derive your satisfaction. I mostly prefer my AG recipes to my extract recipes, but I've made some pretty darn good extract recipes, too. And I don't want to convert them to AG because of the desire for the quick brew day many times. I still get the same satisfaction, though, because I created a good beer on my own.
I would recommend that you assess what you want to get out of homebrewing, how much space you have to devote to the hobby, and how much you are able to spend on whatever upgrade you think will take you to the next level. If it's just a matter of not being dependent on a kit, the quickest and cheapest way is to go extract/steeping grains with hops additions. You can still use the smaller fermenters, unless you also want to double your output, and people have already responded with your options for five-gallon batches.
Don't be bound by what others have done, though. There are plenty of right ways to do this, and with a little research and ingenuity, you'll find the right way for you.