The answer to this question is really “yes” – you do get multiple bonuses if you buy multiple bonus-earning decorations such as Limos or Police Cars. The bonuses work cumulatively – buying two Limos means that you get a 4% bonus, and buying 3 of them means you get 6%. And while the information in the game talks about the 2% bonus applying to all jobs, it also applies to the rent you collect from buildings as well.

That all helps to explain just why players with lots of bonus-earning premium items are able to build up cash as quickly as they do…

To find out what your bonus multiplier currently is, take a look here.