funny "Robocode has peaked" quote
I agree that the game would be much less interesting with visible enemy bullets. However, I don't think that the game would devolve into ramming, or at least, not only ramming at the higher levels. It might make an interesting Robocode sub-species.
Actually, make the bullets visible, crank the gun cooling rate up, and get rid of the turret so that a bot can spit a bullet out in any direction it wants.
With visible bullets, the focus would become (in addition to ramming) the construction of configurations of bullets in air that are impossible to dodge. Pinning the enemy into a corner so that they have limited dodging options would be paramount.
The counter-resonse would be to shoot down the incoming wall of enemy bullets, though this means that one is spending time on defense rather than offense. The refinement of that would be finding the pockets of space-time that bullets could serve both a defensive and offensive function! This would probably represent an investment of processor cycles way beyond what has our bots skipping turns these days.
It'd still be interesting, but probably not as interesting. That information asymmetry really makes things fun!
Visible bullets would lead to perfect dodging or perfect bullet shielding, unless many other variables were also changed, like tick-bullets and bullets which don´t collide with each other, or obstacles in the battlefield.
At sufficiently close range, perfect dodging and perfect shielding would not be possible. While strategies besides rambots might be viable, they would need to be close range strategies.
As an aside, robocode with tick-bullets (even with invisible bullets) could be interesting. With the currently usual bullet power values, I'd suspect that would make it possible though, for bots to make wide enough bullet interesection "shadows" in waves to always stay 100% safe. With smaller faster ones that might not be such a stalemate though.