I've got a few ideas I'd like to see included but I'm just going to post a couple for now.
The first is that I'd like to be able to see the difference suppliers make. Maybe they could be included on the research page, tagged onto the development points line, perhaps in a different colour so they stand out. That way, you can see what difference the different suppliers make. Perhaps even, there could be a confirmation button on the Research page so you can change your mind without it costing a fortune.
Another thing I'd like to see is a way of being able to only partially repair your cars. Let's say (for example) it'll cost you 16 parts to repair your car to 100% so 32 parts for both cars - if you run a 2 car team. What if you've only got 31 parts after watching all the videos? At the moment, you can only repair one car, the other must be left in whatever condition it finished the previous race in.
I'd like to be able to repair 25% 50% 75% or 100% of each car, so if I had 31 parts, I could repair one car to 100% and one car to 75%, that would cost me 16 parts (100%) plus 12 parts (75%) meaning I'd spend 28 parts and have 1 car fully repaired and one car at 75%, of course, you could repair them both to 75% or to 50% or any combination you thought best to get you through the next few races