The question is Is there any difference in connotation between 'ponder' and 'contemplate'?
Although the meaning is the same, the answer to "Is there any difference in connotation", the answer is it depends what nationality you are. In the UK the answer would be Yes (disregarding the persistent degradation of UK English by/of globalisation). In UK English Ponder is Formal whilst in US English it is not. Therefore I would suggest that normally you would not use Ponder in your sentence if using British English.Cambridge English Dictionary
Example
The first issue is to ponder whether it would be regarded as 'evidence' at all?
formal adjective (SERIOUS)Formal language, clothes, and behaviour are suitable for serious or official occasions:Cambridge English Dictionary