I am sorry but i disagree here.
Its not 'entirely' mind satisfaction.
With fuel prices sky high, it is a huge concern for some people. Its especially a concern for people who are still in their student life. (me for instance)
I travel about 55-60KMs daily and i have a CG-125. Because my journey consists of Long "High Speed" patches, fuel consumption is a major concern for me. (Because of High Speed, fuel consumption can increase drastically -- and my bike almost always stays upto 70-90KM/h range)
From a 70cc to 125cc ... the Maintenance & Fuel Consumption is almost DOUBLE.
- While a 70cc can do upto 55KMs easily (even in rough conditions) ... a 125cc can barely do 40KM/L. (which in worse conditions may drop to 30 -- Fact!!)
- A 125cc needs more engine oil means more expense because of that.
- Incase of an Accident, Parts for a 125cc are more expensive (comparatively)
- Tyres/Tubes ... incase of some major damage or wear & tear ... they cost more.
... these are just some highlights.
However, In comparison to "the benefit" a 125cc offers, yes you may call it (the expense of 125cc from 70cc) "not much". (Benefits may include better road grip means lesser accidents & better brakes - No fear of bike shut down in rainy weather, where almost all 70cc fails and refuse to start -- etc etc ... And i did say "in comparison to a 70cc)