Wiktionary lists re as a preposition that means “About, regarding, with reference to; especially in letters and documents”, while OED1 (1914) says:
Re sb² [Ablative of L. res thing, affair.] In the matter of, referring to. The L. phr. in re is similarly used († formerly also = in reality). Re infecta, ‘with the matter unfinished or unaccomplished’, has also been freq. employed in Eng.
Thus, use of re as a preposition meaning about or regarding seems perfectly reasonable to me; it's a concise alternative to regarding, a word which is often used verbosely.
Use re when introducing a new topic. For example, the following would be grammatically and perhaps even stylistically acceptable:
Re item 1, she has no opinion. Re item 2, he doesn't like it. Re item 3, they are sick of it.
Alternative forms of that, with fewer instances of re, might be:
She has no opinion re item 1. He doesn't like item 2. They are sick of item 3.
‒or‒
She has no opinion about item 1. He doesn't like item 2. They are sick of item 3.