Just to clarify some terminology:
The Ritual power doesn't get any specializations. Specializations are reserved for Thaumaturgy.
If you are asking why you would take Ritual Crafting as a Focus Practitioner, I'd say it depends on how your GM adjudicates Ritual.
If you have Thaumaturgy you can create any kind of magic item that Thaumaturgy can create. If you are a Pyromancer, your GM might require that you only be create Fire-related enchanted items. Therefore, the advantage to be a Ritual Crafter is that you can craft any type of item that Thaumaturgy can craft but are limited to items and cannot do summoning or anything else.
Personally, I think Ritual Crafting is better done as a thematic Focus rather than a Type of Thaumaturgy. So you could do a summoning but you'd have to create some kind of item or contraption that summons. It would influence the story of your rituals quite a bit. And, since the book specifically says
Each focused practitioner is different, with
spellcasting abilities centered on a single theme.
(bolded mine) I think treating it as a thematic specialty is how it's designed.
If you don't take it as a thematic focus/specialty, then I think it's pointless. Most GMs let you make whatever items you want, regardless of your specialty. You might as well be able to do fire-related rituals above and beyond your crafting.
Regarding Diane Basset: I have no idea why she'd have a brewing strength of +5. My theory is they added one of her stunts by accident. There's lots of mistakes in the book.
Lastly, if you are talking about Specializtions (like the bonus you get from Thaumaturgy), taking a crafting specialization is useful if you have lots of enchanted item slots since it boosts ALL of your enchanted item slots by 1. Not so great if you only have 2, but powerful if you have 6.
