NOTATIO

What are your thoughts on accents and staccatissimos in the staff? I was looking through the Schirmer Manual of Style and Usage and they said they consider articulations to be part of the notehead and their house style is to place them in the staff if need be, under the same conditions a staccato or tenuto would be.

Only in piano music. I don't like the look of them even there, but pianists apparently can stand them.

I went through a couple of piano scores by different editors (some Ravel and some Prokofiev), and so far only staccato marks were used within the staff, everything else was above or below.
I'm not a fan of the look of accents and such within the staff. I find it makes the staff look cluttered and is, honestly, harder to read.

I agree with both of you. I don't recall ever seeing accents in the staff and it doesn't look right to me.

besides, from the Schirmer scores I have, they are THE LAST people I would look to as any sort of reference in engraving. Most of the score they do really are badly engraved.

I don't know if I've ever seen a Schirmer score, but I came across there style guide recently and found it pretty standard in most places but eccentric in others. For example, they don't apply trill lines unless the note is tied. Even if it's a whole note, it doesn't get a trill line.

I don't agree that G. Schirmer editions are badly engraved. Their beautiful plate-engraved late 19th and early 20th century editions continue to be used today by many musicians. And the later editions of American classics by Barber, Bernstein, Corigliano etc. are models of editorial excellence and some of the most beautiful produced by a US music publisher (example from Barber's Piano Sonata):
I don't have the Schirmer style manual, but the original example seems to relate to cases where the the accent mark is forced to be far from the note head or beam so that the connection between the note and the marking can begin to be lost. The same arises with fingering at times. In cases of this type, the manual apparently feels that it is better to place the marking on the staff as the lesser evil. I think that that is reasonable approach.
The system of restricting trill extension lines to tied notes is an older system. It avoids unnecessary clutter and has a lot going for it.