score:2
There are no rules restricting how you travel using your Schengen visa. There are rules telling you where you should apply for it given a particular travel plan.
Since you have a multi entry Schengen visa, it is perfectly fine to make a trip to Malta, and later a trip to Spain. If "they" would mind you making multiple trips, they could have given you a single entry visa instead.
Now what you should not do is apply for a Schengen visa from the Spanish embassy if you actually want to travel to Malta (and not to Spain). You didn't do this, but there might be a risk that the Maltese border person questions you on this. Having evidence of your subsequent trip to Spain on hand and being able to explain the situation should alleviate this.
Getting tickets you don't plan to use just to paint a particular picture seems like a very dangerous idea to me.