I use a splitter and do not seem to have a problem with range. We 'see' ships at more than 20 miles. Certainly not a scientific experiment since there is no control for comparison with two antennas. The idea of having a redundant antenna is attractive though.
Back in the water in Grenada - with new main and #2 and cockpit canvas (Santa came early). Will spend the winter and early spring in the Caribbean and then head to Bermuda and the northeast US. Still trying to decide if we will bring the boat to Canada, either in 2015 or 2016.