The older style baseboards where wider most likely due to ease of access to run electrical lines. This was a common practice in the early 1900's to the 1950's and beyond in some areas. Nowadays we all know outlets need to be centered 12-18" off the ground in most cases. Having them on the moulding is no longer acceptable.
It also was a lot of just the type of trending style at the time. Now it looks gawdy. If you are spending any sort of substantial time and money on drywall and such, just replace it. It is not hard to make miter cuts, I believe you can even rent a miter saw at a big box store. Trust me, you WILL break some of the moulding..and then you'll have to conjure up a replacement which will not match the original exactly. It's up to you but this is just my two cents, best of luck!