There are always people who are spending more than you, no matter how much you spend.
If you really like the game there is nothing wrong with spending some money on it. However, it is also totally possible to play the game very successfully without spending a dime. Make sure you read through the forum, especially the tactics and tutorials section, to get the most out of your ressources.
Me personally I only buy the special sponsor every season for 5€, as it is the most valuable asset available for that price.