Most of your channels come from the south (around compass heading of 172ยบ). There are a few channels coming from north of you, but you are right that they are mostly just duplicates of network stations you already receive from the south. Unless you have a pressing need to get a particular channel from the north, then I wouldn't bother trying since you already have a pretty good lineup of channels.
Splitting the signal does lower the power reaching each tuner by a little bit. It's still hard to say whether or not you will have overload issues on any of your tuners because you are starting with some seriously strong signals. You might want to try a signal attenuator (like the one mentioned in my previous post) to see if it makes any difference.
BTW, most splitters come in powers of 2 (that is, 2-way, 4-way, or 8-way). If you are using a 4-way splitter to go to your 3 tuners, then please be sure to terminate any unused ports (you can use inexpensive terminators like
this). Open ports on a cable network can cause signals to reflect back into the network, which creates signal "echos" (a form of interference) that can degrade your signal. If your splitter really has only 3 ports, then you don't have to worry about this (most 3-way splitter are really 4-way splitters internally with the extra port terminated inside the case).
If you are daisy-chaining two 2-way splitters, you also don't need to worry about termination (since you have no open ports), but note that one cable path only goes through 1 splitter while the other two paths go through 2 splitters. The path going through just 1 splitter will have a slightly stronger signal than the other paths.
