I am glad you are happy with your pocket rocket.
my views differ slightly.
1) Sound does not goes down, You get used to it (can recheck with a instrument to check noise levels)
2) Engine oil change cant do anything about gear changes being smooth, System and you are learning each other (only if Suzuki put in the wrong oil and replaced it with right gear oil, That would make a difference).
3) My AGS used to jump up gears as quickly as it could, At times i shifted to manual to hold gears, (often at intersections, it upshifted and you loose the push you need to cross a intersection quickly. Just like it would upshift coming out of a basement (that too needs manual 1st gear to come out.)
4) As long as you are happy, its fun to drive in the manual mode, but you cannot achive the economy AGS can provide you, Since you are getting better average in manual mood, Stick to it.
5) Yes, as mentioned in point # 3, It quickly shifts up
6) For overtaking, Always use manual mode, in automode, as quickly it down shifts, it upshifts as quickly too, Which can be dangerous if you are overtaking an over speeding car. (it does goes up to 80 and 100 speeds really quickly, Uskei baad iski jaan nikal jatti hai) , I remember give a CVT Vitz run for its money, and all 4 people in my car had a good laugh, Vitz wala kia samaj ke daddo se race keraha tha)
Alto is a fairly nice car, spare parts are decently priced, AGS maintainence in the long run would be troublesome. And i dont belive it is a safe car. Its very tiny, very lightly build, It shouldnt be allowed on motorways.
This is ok for a city car. a small hit can damage its front bumper, Radiator, Condensor, Compressor, a bike hit can cause serious damage aswell.
Not taking about airbags, But i wont trust a Alto with my family.