You could save the values in an XML format. You could save Text to an element and you could save FontWeight to an attribute. Get them both from textblock.
Also, since TextBlocks can contain text with a variety of formatting, you might want to look into TextBlock.Inlines, which will help get the formatting of TextBlocks created like so:
<TextBlock Name="tb1">
This has some <Bold>bold</Bold> text.
</TextBlock>