IMO it depends on the direction you want to take him from here.
If he is a speed/elusive back, which it looks like he is, and not a balanced, then strength is not that important at all. It really helps prevent fumbles and has a small chance to help break tackles for an elusive, but not much and not like a power back. He doesn't seem like he has any issues fumbling the ball so strength is ok, and carrying should be fine too for the same reason. Carrying also helps trigger SAs but since you aren't investing then again it is fine for now.
If you want him to be an every-down back, then you will definitely need to work on stamina so he still has a good burst and speed in the 4th qtr. Confidence has been retooled a bit making it more important for things like fumbling and again, breaking tackles. I would work on it a little bit but it's not a priority since the SA thing again.
I would say your best bet if you really don't want him breaking tackles and investing in SAs, is to work on vision primarily with a second emphasis on stamina. Keep going with speed, but you can slow down on agility a bit, low 80's is more than enough until mid 50's. My back is 111 speed/92 agility for example so I subscribe to the 20 points less of agility theory.
I would suggest starting to invest in your SAs though, things like quick cut and first step aren't wastes of skillpoints at this point in your guy's level. It will only help bolster his natural attributes/agility for acceleration and directional ability.
