I probably replenish at about 2X the rate you mention. I have noticed (especially with low amounts or restrainer) that there will be a bit of contrast drift in fairly short order, and it is very hard to maintian consistancy without dilligence.
You threw me a little by using the term 'topping off', because that implies that all you are doing is adding more developer to maintain a certain amount of solution. I generally will siphon off some developer every few prints and mix in some fresh. Typically, I'll pour off the top to keep, and the pour out the bottom where all the buffers and other contaminants have settled. Then, I'll replenish with fresh developer and add the dichromate needed.
I don't need to filter the solution this way, and even though I keep it hot, it is covered, and I rarely have any devloper drop crystals out when it gets cold. Ultimately, there is no reason to be working with the developer anywher near the saturation point. I mix mine to about a 20% solution.