18 yrs post op LASIK, is +5 worth it if it fixes HOAs?

I assume you have no refractive error (nearsightedness, farsightedness or
astigmatism), and that your night side effects are purely due to high order
aberrations (probably lots of spherical aberration) from a small optical
zone. If this is the case, your doctor
is partially correct in saying that further LASIK (or surface ablation)
treatment to address the HOAs will leave you hyperopic. Exactly how hyperopic you may end up is
hard to predict. If your corneas
are sufficiently thick, you could consider a second touchup to address the
consecutive hyperopia that will likely develop.

However, what your doctor has failed to mention to you is that there is a
new, FDA-approved laser treatment called CATz, which is a topographically
guided laser used for LASIK. The
laser, manufactured by Nidek, can treat higher order aberrations without changing
the spherical equivalent (nearsightedness/farsightedness). In other words, the CATz treatment will
be much, much less likely to leave you farsighted than would a standard
wavefront-guided treatment.

There are eyedrops such as Alphagan-P which are helpful with night glare
and halos. These drops work by
constricting the pupil and effectively reducing the HOAs in your optical
system. Of course, the effect is
temporary (lasts approximately 4 hours), and reducing pupil size at night can
reduce contrast sensitivity and overall quality of vision. But, many patients find the tradeoff
well worth it.

If you do proceed with surgery, you may want to try one eye at a time to
make sure it addresses your problems and any tradeoffs are worth it.

The problem in treating patients with small optical zones is that removal of tissue [depending on the higher order aberrations] might make you farsighted.  This could end up causing more issues with worse vision at all times, even though you might be correctable with glasses, you may end up unhappy. A PreVue lens can be made to determine whether treating you might help.  If a Prevue lens clears up your issues, it would be worth a try in one eye first, then the other eye. Surgery would not be the first option.  Other options might be to have a contact lens made that is actually molded to your eye. These lenses are new and might be effective as well.  Once you got a contact lens that helped, you could further reduce night symptoms by coloring the lens to effectively reduce the pupil size. These things are not standard and might require a higher cost but might help. 

Small optical zones are notorious for creating quality of vision issues such as those you are currently experiencing. After a full evaluation, you might be a good candidate for a revision procedure making use of custom wavefront laser treatment. I don't understand why you are being told that such a treatment might result in that level of hyperopia. Your evaluation should make use of a Prevue lens to predict whether or not such a treatment might address your ongoing visual complaints.