Ok - here's my ideas and i'm not a Town Planner. Look, I was born and raised on the common, i know every hillock and every blade of grass - I even know where the ground markings showing the roman building that was up there. I love that common, and spent a large part of my youth chasing people in cars off the common. However, this is the only answer I'm afraid. A nice neat tarmaced parking area with trees/hedges etc.
Car park could be used for a number of purposes
1. Parking to walk into the village
2. Parking to go to station or bus on Cardiff Rd
3. Parking to take children to swings and to play on common
4. Parking to then walk up to Rugby and Cricket Club
Stop traffic going up Southra all the way to the club-
Put in a proper tarmac path through to village and (maybe) rugby club.
Improve the pathway from Common down to Station Rd.
People dont go to the village to shop because its so dangerous with the way the traffic goes through there. Let traffic come down from the Mount Rd and turn right into Station Rd. Stop traffic apart from delivery vehicles going to the shops and maybe there should be tme limits eg deliveries must be completed before 10am.
Traffic can come down Britway Rd but not turn right at Twyn. Make village pedestrian from Britway Rd end (by the cenotaph) to just before the inter-section of Station rd and Mount Rd.
You could have parking for about 80 to 100 cars on the common, south east of Southra. The pedestrianisation of the village would attract more retailers and shoppers. It would put some heart into the village. Get the village better policed at night-more people will come down for a meal and a drink - get rid of those Indian and Chinese restaurants or improve the quality- the food from both is crap.
Car park could be ticketed with free/reduced charges for Dinas Powys ratepayers displaying pass. That would stop people from Sully or Barry parking there to catch the trains. You could even have some areas of the car park with all day parking and other sections with 2 hr limits.