Perhaps it's because the Vectrex was not so popular and marketed only in small quantity (no one knows exactly, but certainly under 500000 pieces were sold, see details here: http://atariage.com/forums/topic/59575-vectrex-numbers/
Only a few people owned this console, and have nostalgic memories about it.
It's rather a unique piece of hardware with it's vector graphic, and a curiosity instead of being a true mass product.
Your work is highly appreciated, and it's value cannot be measured with the numbers of replies! It's about preserveration of a small piece of the gamer history, and valuable for the future generations.