Don't go for cultus whether you keep passo or not its up to you, you'll face these issues in cultus for sure if Suzuki didn't rectified them.
1. A/C problem in hot summer, I faced, my other two relatives faced the same, wagon r's A/C is very good but cultus A/C is bad in hot summer.
2. Noise from front suspension, it has faulty lower arms which Suzuki is unable to rectify only they change control arms which is temporary solution, I faced it after only 3000 km of drive.
Other than these issues its interior quality is very cheap even cheaper than wagon r's, door panels feels like made of gatta which rattles very early. Cabin is not quitter at all, alot of road noise there.
Fuel economy, pickup, ease of drive are its plus point, also brake is good.