Is there an improvement braking from the hoods from Shimano Sora 3500 to Sora R3000?
The R3000 levers have the shifting cables routed under the bar tape as opposed to coming out the sides on the older 3500 levers. If you care for the esthetics then that might be another reason to upgrade.  I'm not sure if the  braking performance actually changed as I don't have older Sora to compare to, but the R3000 levers in my experience seem to offer good braking performance from the hoods. The design of the R3000 levers is similar to the other higher tier models (tiagra, 105, etc) so I assume that the braking performance would be the same as those, assuming the brakes at the other end of the cables were also of the same quality.