Thinking about options for getting a VHF/UHF antenna up there. However, the feedline, which is RG213, is about 150' so over 3dB of loss minimum.
So the first question is, does the current antenna go through
the same 150' of coax and the switchbox?
If so, then the loss in the cable is a constant, and doesn't factor
into the comparison. If not, then we need to figure the total
difference in coax losses as part of the calculations.
WB2WIK used to say that no feedline was too long if it ran
vertically. That is, the gain due to height is more than the
losses in any reasonable feedline.
I have some sample numbers for relative gain over a 10 mile
path on 2m, but they only go up to 40'. I looks like the gain
is about 2 dB going from 30' to 40'. Even RG-174 would still
show a net gain at that point (it has about 1 dB loss in 10').
That's not to say that you should use lossy coax: use the lowest
loss type that fits your budget. But the added gain due to
height will often outweigh the loss of the (vertical) coax.
But there are other factors to consider, too: your operating
preferences, local terrain, and local repeater locations.
I live in a valley, and my primary limitation is topographic. I have
good coverage of surrounding repeaters (mostly on the surrounding
hills) with a low antenna, but I can't raise it far enough to clear the
surrounding hills. So a higher antenna, or higher gain, won't make
much difference on many paths.
If you are already on a 5000' hill, the net change in height may be
insignificant (once it is high enough to clear the edge of the hill).
But over flat ground, tower height can make a big difference, and
you probably would want to do some modeling to see how much it
improves your signal into other area repeaters (or to local towns
with simplex activity).
That, of course, assumes that you are operating FM, which is
likely given your current antenna. For weak signals modes
like CW or SSB, height is even more important, and you'd
want a horizontally polarized antenna, probably a beam for each
band.
My current VHF/UHF antenna is a coaxial vertical (AR270B) at about 30' fed with LMR400 and it works pretty well hitting repeaters over a wide area.
The AR270B is a "collinear antenna", but not a "coaxial antenna".
It's the same principle as the old Ringo models, but the old ring
has been replaced with a sealed pre-tuned matching section when
they converted it to dual-band operation.
Probably would have better decoupling on 2m if the radials were
19" rather than 6 1/2", but that seems to be a change that a lot of
manufacturers are making on their dual-band antennas to save cost.