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.
Heading back to Lake Ontario for this summer. Relatively few stops along the way from Grenada. Martinique, Guadeloupe, St. Martin (must have something to do with the French food), then Bermuda, New England and up the Hudson/Erie Canal. We were going to go via Newfoundland and Labrador but June remembered that one of the kids is getting married this summer - details, details!