I'm writing sci-fi/fantasy. An artist friend has offered to illustrate the manuscript with b/w line drawings. Maps and illustrations. He's pretty good, he's been a NY professional illustrator for 30 years and makes a living at it.
My question is whether agents are likely to appreciate this effort? Or do they tend to think all such things are in the domain of the publisher, and they're only interested in the words?
Unless you are submitting a graphic novel or a picture book, you don't send illustrations with a query. For starters, illustrations would have to be attachments and most agents specifically say "do not send attachments" with a query.
Secondly, most SFF books are not illustrated. Illustration adds to the cost of book production, and most publishers are trying to keep costs low, particularly if you are debut novelist.
Third, you haven't mentioned money, but unless this artist friend is a Very Good Friend, and or your spousal unit, the question of making money from his/her art and not compensating him/her is going to be tricky.
Here's what you do: you say thanks, and mean it, for a kind and generous offer. Then say you know you can only send text in a query but if the opportunity arises, you'll be honored to mention this offer to the publisher.
This kind of offer of help happens a lot to writers at the query stage. Well-meaning friends and family want to help but they don't know enough about how publishing actually works to offer usable help.