An outside, amplified antenna is certainly not a cure all for instant, strong, fast internet.
But after 2 trips between NJ and Florida...my antenna has saved the day for getting internet in dozens of location. One of the most notable was the Mega Dock in Charleston...sure they have antennas and good signal strength all over that HUGE marina but the speed was so slow we were gonna slit our wrists using it. Because we stream Wifi to Skpe our kids, watch television, and overall entertainment in many forms...we are usually happy to get good internet without paying a fortune in monthly data plans. With my bullet rig I was able to pick up an unsecured wifi that had to be a 1/2 or more miles away (so some range extension is necessary) that worked fine.
I find many marina HAVE Wifi but it is so slow that they might as well not advertise. Can I always get an open signal?...no...but in more than half the marinas and anchorages (picked because of available Wifi) I could because of my setup.
Is it worth $300 up front and possible need replacement in a few years (mine is on 24/7/365)?
To us it is...but I can see maybe not everyone.