John, forget the LMR, will not get you anything at these frequencies, especially if you are running quad shield RG-6. The difference in loss between the two with your length run is only 1.5dB or less, which is barely the difference between breaking squelch and not. The first thing you need to do is decide how important the UHF is to you... if not that important, you have better options, firstly being the antenna. What we need to do is plot the distance and azimuth of all the stations you need to pick up, the frequencies and the relative strength observed of each station, strongest being a "10" and working down, in fact just dividing into four groups, "full quieting", "solid copy", "noisy" and "Can hear something if I open the squelch" is enough for the survey. Anything "not at all" with your current setup is not likely to ever be brought to "solid copy" without an extraordinary deployment of money and effort. You plot that map, then we determine the ideal pattern that would "normalize" the signals all around, then design the system needed to achieve the objective.
For example, if you have solid copy of the local CTAF's including planes on the ground, and the gain to the ocean needs to be bumped up a couple dB to make the ground more solid, the solution could be as simple as a ground plane antenna side-mounted on the mast at the proper azimuth and spacing. On the other end would be a superior omni antenna like a j-pole or sleeve dipole for the CTAF's with a two element beam aimed east for the oceanic stuff, since most of the traffic is there anyway. More exotic solutions can combine the two into one, such as a beam (or 2-el phased array) with an additional offset parasitic element to distort the pattern and give you two gain lobes, perhaps one due west with 6dB gain for some local airport and another to the southeast with 8dB gain for some other airport or region. Anything can be modeled and anything can be built for little money, so we just have to determine the requirements and the rest is pretty easy.
You've already got your antenna up 25-30 feet I suspect,unless you at least double the elevation you will be dismayed, and at double the elevation you will not be impressed, either. Unless trees are an issue there really is no difference until you go from 30 to about 100 feet and/or above surrounding trees,in terms of your effective real-world radio horizon, and even there one or more directional arrays are easier and cheaper. It's not that I am against maximum elevation, it's just when you are already at around 30 feet or so (verses ten) you really need to triple to get a worthwhile return, so the expense of a typical 50 to 60 foot tower is simply not worth it (especially to a spouse) unless you plan to hang lots of other stuff up there. You also significantly increase, like by as much as ten-fold, the likelihood of a direct hit since you now are competing with utility wires and poles for a dose of the Wrath of God.
Another upgrade would be using a better preamp, like those from Advanced Receiver Research, designed specifically for the band (which is why you have to decide about UHF), mounted right at the antenna and powered via the coax. That will give you 20dB to offset the -3dB for the coax run and -6dB for a 4-way splitter, giving you around 10dB net overall gain, which is the most you should consider when you are using consumer grade equipment (scanners). That preamp may even be selective enough to eliminate the need for that stub.
If it were me, the first thing I would do (after the survey) is go with the preamp, because that would be a keeper, basically essential given the length of your down-lead, and an integral component to any eventual solution.
Anyway, that's my take on it, and that's all for now.