You might not value your own work if:
-You pay for ingredients out of your family grocery budget and count anything you make as "profit" (I refer to this as grocery store money laundering).
-You don't know off the top of your head what your overall profit margin is.
-You "throw in" extras without charging for them because you want to be nice.
-You have people tell you that your prices are "very reasonable" all the time. That means that they're too low.
-You're afraid to actually keep track of how much you work because you know that if you did it would make you depressed to see how much (i.e. how little) you make an hour.
-You're fully booked every week and it's getting to the point where you wish you weren't. If you book every single piece of business that comes your way, your prices are probably too low.
If any of those apply to you, you should probably either put a minimum into place, or raise it if you have one. Having a minimum order amount will help you psychologically value your work, and if you value what you do then other people will. You have to be willing to hold to that minimum, though, no wishy washy "well just this once" stuff, my friends. No, no no, you need to be strict with yourself about it.
-Minimums screen out the bargain hunters. Enough said.
-Minimums make sure that you're going to be paid for your time (as long as you've priced your cakes correctly, which is another story. But at least you'll have a better chance of not being paid $30 for 5 hours of work.
-Having a minimum communicates to the customer that you're not an "off the rack" baker, and that you value your own work. And that's the key to being paid more than minimum wage.
I recently raised my minimum wedding cake order to $500. I spend the same amount of time on planning, shopping, baking, and communicating with customers for a small cake as I do for larger ones. There's a small time savings on decorating smaller cakes depending on the design, but that's not always the case. So basically, a tiny 5-7-9 wedding cake, once I take the time that goes into it into account, isn't worth pricing it by the serving to me. A minimum will basically make sure that I'm getting paid for my time.
So if you don't have a minimum, try it. You might lose some customers, but chances are the people who DO value your work will tell you that you should have raised your prices long ago, and those are the customers who you want.