I have an old pair of Effinghams (pull ons) that I've had since I was 9, 17 now AND they were bought used. I love them and will never sell them. I school in them now. I just got a new pair of the Mountain Horse Venice ones that the OP posted earlier. I went to Dover and I cannot believe how different the zip ups fit. They aren't baggy, which pull ons tend to be like, because the zipper allows it to conform better because you won't be shoving your foot down in them. The dislikes are that the leather does not shine up very well, at least I haven't gotten them to yet..my Effinghams shine like glass with minimal effort. And the Venice have the weird elastic thing, which is a big help to me, because I have a runners calf (slim ankle, then big round calf muscle :P) which is fine for showing, but it takes away from the smooth look of the boot. The foot is so comfy though because the sole is a softer rubber, so if I wear them around all day, my feet don't get sore. They are still in the breaking in stage though, and are fine to wear before I ride and during, but after they hurt around the ankle so bad :(
You said you liked the Spanish Top style...personally I haven't seen pull ons like that. I think that is because the only pull ons out there, tend to be more traditional, or if you buy used, they are older, and the spanish cut style is fairly new..at least that's what I think.
Why exactly don't you want ones with zippers? Think about this, what if you fall off and break, or potentially break, a leg or ankle, and you have pull ons? They will cut them off. But more than likely if you have zip ups, you won't be out an expensive pair of boots ;)