Let me preface this with I don't always know what I am talking about:
I think, depending on the condition of the books you bought, you would make more money in the long run with slabbing. People like the security of knowing the grade of the comic they are buying and are willing to pay for that security. However, I don't know what shipping rates to CGC are from overseas so I don't know if it would be cost effective for you to do it.
With the market the way it is on these books as of right now, it doesn't seem like from what you say you will have a problem making your money back or even turning a profit. Plus, it brings you enjoyment.
I say it would make more in the longrun, but you have to decide if you want to/can go through what it takes to slab them.