I encourage either prolific submitting or highly targeted submitting. Editors have taste, vision. They are artists, just like us, and their mag is their artistic product. Even if what you have is really good, it often isn't going to fit into their vision of what the magazine is supposed to be. I'm more of a prolific submitter. It's worked decently for me. My sister does targeted submitting. Reading a mag, figuring out whether she likes it, whether or not the editors have similar tastes/vision to her own and then submitting. I prefer scatter-shot submitting because I've yet to find a magazine besides Strange Horizons that fits inside my own tastes. Unfortunately, Strange Horizons are very liberal, and I'm not. And the more experimental my writing (aka, the closer it gets to what SH publishes), the less liberal it becomes.
I discourage highly-targeted submission. Not because it's a bad idea, but because it's time consuming, potentially costs money, and ultimately rests on trying to intuit editors, which is something I don't actually think most writers are very good at. Looking at the kind of material a magazine has targeted in the past can be helpful, but editors can be fickle and their tastes may evolve over time and, ultimately, if they are after something 'different' then all that research may actually work against you. Additionally, I do not believe that targeted research is more efficient in terms of time or more likely to yield success than simply submitting to everybody as expeditiously as possible. But I don't know. How many stories has your sister published, out of curiosity?
Also, what do you mean about Strange Horizons being liberal? What does 'liberal' mean in this context? It's such an abused term these days.