The bottom line is... I can see great value in being able to fly by instruments in situations like these.
You can get that kind of training without getting another rating/certificate. Just get a CFII to work with you, explaining what you're after, and spend some time (and money) getting the training you want. It also wouldn't hurt for you to, at the least, go to the FAA website and study the relevant sections (perhaps under the guidance of the CFII) of the Instrument Flying Handbook. Or, if studying on the computer isn't your thing then you can pick up a paper copy at Sporty's or such.

Having said all that, if it makes the temptation greater to fly in poorer weather, then you'd be better off getting the rating. The knowledge and skills you develop in doing so make you a better pilot*, even if you never use it again, much like learning to fly a taildragger improves your skills, even if you normally only fly a tri-gear.

* Yes, even learning the approach procedures and working with ATC help your flying, at least partly because you get your cockpit tasks better organized and learn to deal with some awkwardness, distractions and tasks in the cockpit under both visual and non-visual flying.