As someone who has used both stations for commuting and travelling in all available directions from Worcester for well over 15 years I can categorically say that both Worcester stations need the order to survive. The thought of closing either, even with parkway, doesn't bear thinking about.
Foregate, you could say serves those (like me) living to the west or in town who commute out (Birmingham in my case), or those who work in the town that travel in. Closing foregate then means that you are inconveniencing hundreds on a daily basis who would have to sail through the former station and take a separate mass transit route back or walk through a less than nice part of town. There are several schools within 2 mins of Foregate so you now have a hundred or so young children displaced twice per day. Will an alternative method of traveling between the two stations be capable of taking a trainload around the corner in one go?
Shrub Hill then caters for those who drive to the station, park at it or near it. Those in the East of the city would be closer, I used to live over looking the sidings and this was my closest station by a few yards. The station is exceptionally busy during the peaks and during the day it is a surprisingly peaceful place to wait for your train and watch the freight go through.
There are 5 platforms at Shrub hill (1 A/B, 2 A/B, 3). Not unusual to see all platforms occupied in the peak. Platforms 1 and 2 can take an HST with room to spare, platform 3 is a little odd, mostly used for stabling now. The old motorail platform is still there - shuttle to parkway any one?
There then is the significant amount of sidings available, it's a busy enough yard. Diesel depot, stabling for GWR, through roads for freight, heritage trips and operators use i often. Then the fairly large drivers and guards depot will need housing somewhere.
So what if Foregate is a parasite on the face of shrub hill, both need the other to survive.