Cultus low top speed and low pick problem

I have Cultus 2006 (non EFI) and it did around 150,000 km approx.

The problems I am facing are:

1. Low pick (acceleration). Engine sounds ok. But I feel that the car is moving like a dead man.
2. Low top speed. On motorway (Isb-Lhr), it hardly crosses 100km/h at CNG. And max 120km/h on patrol on the straight road. And on slightly high road, dont ask.... its like 60km/h.
3. Last week I went to hilly area (peer suhawa), the drive was really pain in the a$$. It gave me very tough time during the heights.

I did 140 km/hr on CNG and 160 km/hr on Patrol before on motorway and drove to murree, azad kashmir and pir suhawa without any kind of problem !!!! but now it really sucks!!!!

I just visited Suzuki 3S workshop and told them the 3 issues above. One of their technicians did a test drive. He also observed that the engine was vibrating when it started on patrol at just 1200 RPM. Anyways he told me that there is a problem with valve pressure. The valves are leaking and the pressure is not building up, that's why it is not giving max performance on pickup and top speed. Their supervisor also came and observed. They gave me an estimate of Rs. 29,000. Below is the list of things that need to be changed (if required), as it is an estimate only.

* valve set
* valve guid set
* valve seal set
* thermal state valve (std)
* head gaskit
* silicon tube
* radiator service
* timing belt + bearing

The car had an accident from front around 6 months ago, so I assume that these might be the side effects of that accident + 150,000 kms driven.

Did any one of you experience similar issues with Cultus?