Hi Neil,
Not sure how you've set up your HDRI, but the background does not help your image.
If I was you I would keep things simple to start with & switch off the HDRI settings, still keep the direct light with vray shadows & use a nice landscape (trees/sky) background in the max enviromental slot.
Try looking at improving your textures, the brickwork map (std autodesk brick map) is way too large & the grass / paving could be better. Plenty of texture resources are available.....listed here on CG Architect
Once your happy with your standard direct lighting & textures, THEN start experimenting with HDRIs....again there are many tutorials & techniques on setting up HDRIs
Good Luck & keep posting your results