Upgrade: Speakers or Amp. mod?

I have an Onix SP3 which I love. I recently decided to have it modified with better caps etc.
However, a pair of speakers have recently been put on sale at Audiogon which are the next model up from the version I currently own and also really like.
Which upgrade would you make? Should I have the amp modified or should I upgrade the speakers?
I cannot afford to do both now.
I await your replies.