Your pricing seems good - the competition in the area is not as good as your house (they are all terraces/semis which also need cosmetic updating) . Poor photos seem common to the area!
Space is a bit unbalanced but woudl work for people needing something like a home office or home work area, teenagers or an elderly relative.
TBH I would just do the following and not spend much money as you are in the right ballpark for houses around you.
Declutter.
Give the place a bit of kerb appeal with some plants/flowers out the front.
Dress the sun room as a dining space and portion off the utility area (an ikea 5x5 kallax would work fine for this)
Kitchen have a couple of bar stools at the peninsula and maybe a couple of comfy chairs/sofa against the back wall to be more family/ social space.
Retake the bathroom photo, its rubbish angle and there is stuff everywhere.
It is a shame you can't go directly from the garage extension into the back extension room - you could have done the bathroom in a long thin line and had a corridor there. Then it would have had the potential to be a self contained annex type thing.
Anyway it doesn't look bad at all compared to the other houses near by!