Remember that your #2 Nav will have a localizer anyway, which means that you have a backup means of getting via a VOR or LOC approach (or simply ILS without the GS, which will have localizer-only mins). You probably won't be flying when it's actually mins out very often. If you are, then it might make more sense, but overall it probably won't be an issue. Your 430 probably won't fail (they have a good reliability record), and CDIs are also typically pretty reliable. So even with those as your two potential failure points, it's rather unlikely you'll ever have an issue.
We are installing a 430W into the 310 to compliment the 530W as I type this (well, someone else is doing it, and they're probably taking today off, but you get the point). We do fly when it's mins out reasonably regularly, and we also fly in areas where losing a GPS would be pretty bad due to lack of radio communication and no approaches to get in other than GPS for 100+ miles. We also have an Aspen which, while it's a great tool, proved less reliable than our 530 when it let out a poof of smoke and quit working somewhere south of Cozumel, Mexico, also meaning that I didn't have a means of getting the 530's display on a CDI.
My suggestion is to stick to the single GS. It won't increase the value of your plane when you go to sell it, and when you move up, then you can consider having a second GS.
