Car with EGR and without catalyst

TL;DR

• Mercedes 250 diesel 12/1995
• Rode 350.000km always in low revs
• Feels clogged, low power
• Disabled EGR, empty catalyst

Questions:

• How to restore power to the engine
• Should an EGR be active without a working catalyst?

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My car is a mercedes 250 diesel from 12/1995. It was from my father, who bought it with around 250.000km. At that point it had immense power and would easily accelerate even while climbing steep hills. Shortly after buying it he had the EGR disbaled (it is there but it was clogged/covered from the inside so it does nothing). I am not sure if that caused a power drop or not. More recently (about a year ago? maybe more) he had the inside of the catalyst emptied. It ran until 600.000km, mostly doing city circuits and my dad very very rarely hits the throttle, so the car always felt clogged, with low acceleration and reduced strength.

The car became mine about two months ago. I rode hard for some time and I still push the revs from time to time so that the accumulated soot and thrash gets cleaned. Right now the car feels a lot better (before it didn’t even get to the redline in third, now it gets there in any gear up to fourth – did not try fifth) and smother, but I still feel that it lacks power.

I am no mechanical engineer, but I guess the engineers who balanced the engine with the EGR and catalyst knew what they were doing and the engine should have more power with those two components working correctly. Maybe I am wrong, but I did not find a consensus in the large series of questions on this site and others discussing whether the EGR is positive or negative for the engine.

Getting to my question. First, I would be grateful for tips on how to restore some power to the engine. Most likely it would need some deep cleaning since it ran some 350.000km constantly in low revs. Can something along these lines be done cheaply?

Secondly, I am considering to see if the EGR can be reactivated (following the reasoning above) and also due to environmental issues/regulations. Although I would like a definite answer on whether it provides more performance or not, my concern here if the EGR can “work” with an empty catalyst, or if it would cause a catastrophic amount of “trash” being sent into the engine. My reasoning is that if the EGR will bring unburned particles and “trash” into the engine, it would be even worse if these particles are not processed/cleaned by the catalyst.