It made more sense when it was originally added. It gave you access to an entire second map (the Facebook server). It had a different tileset and some minor differences. But it had its uses (one random example: When the token shop opened, the guy gave you 15 free tokens. If you went on the FB server, you could get another free 15 tokens). And the low player count was obviously a very useful factor when it came to times you wanted to do some type of farming and not have to deal with a bunch of other people (for example, there was a time baddies dropped tokens. Swamptown was one of the best places to farm for these given the large amount of baddies and a high spawn rate, but it was always pretty crowded, hence the FB server, which rarely had more than 50 people on).
The VIP items can be fun. The extra colours are nice. But Oasis doesn't really compare with the old FB server. Yeah it's great for bug catching, in the spring and summer. We're in Fall now though so that purpose is pretty much gone. It has some nice shops, but once you buy what you need, you don't necessarily have to go back.
I agree there's currently not enough incentive to have a VIP subscription.