Lol! You’ve already answered your own question, @lynncoyle.

So, do I start commenting less, to try and write more posts of my own? That doesn't seem like the right choice to me.

So, you shouldn’t. Simple as that.

IMO, reaching 500SP is only considered to be such a milestone because you get the official slider. But there are plenty of other ways to spread your votes before you have 500SP.
So it is actually not such a big deal.
Oh, I forgot: you become a minnow instead of plankton/redfish at 500SP. Tomato, tomato (Right, that only works when you say it out loud, not when you write it, lol)

I can definitely relate to the issue of not having time to write your own posts. I try to follow up on so many people, and to reply to all comments I get, while trying to find some people that need a little extra cheering , that I often don’t have time left to write a decent post. Because most of them take me several hours to get them ready to post.

Fortunately, I live in a different time zone than most people on here, so I regularly take the morning off to write my posts. But while I’m writing, I’m aware of the fact that comments and posts-to-read are piling up again...

Bottom line: you should do what feels right. SteemIt should stay something you enjoy. If not, I guess you’ll get tired of it soon.
Don’t focus on those milestones. Or if you do, then turn it around in your head: you started with something like 15SP, and now you have 350SP. Way to go, @lynncoyle1!! ;0)