If you are happy enough with your PRS350 (although a couple of years old, it's not exactly slow is it), I'd at least wait for a while until they iron out issues with the first batch of lighted readers. Unless you are really desperate for a light that is.
Although in saying that, if size is the issue, the Glo isn't really that much bigger in size & weight, it's a bit smaller than the likes of the T1/2 and the Kindle?
PRS 350: 145 × 104.3 × 8.5 mm, 155 g
Kobo Glo: 157 x 114 x 10 mm, 185 g