The image of a metaphor is strengthened if
7. it is somewhat common.
You want to reinforce the notion that love is ubiquitous and that your relationship thrives in the every day. Marriage, after all is an every day activity. The metaphor you choose to illustrate your love in your wedding ceremony should be frequently encountered.
If something is too exotic in your life, then your chances of encountering it are slimmer. You loose the reinforcement that common activities offer. So using an image that involves the life-cycle of a camel if you live in Rhode Island, even if it can be made gloriously beautiful, is not going to provide the daily reinforcement that the tides of the sea or the changing of the seasons might.
Tip: Choose a metaphor to describe your relationship that has value and frequency in your life. Then it can be something more than poetic beauty, it can be a marital aid.