There's really no good beaches on Bonaire close to the vast majority of the dive sites. Pink Beach might be one exception. A couple of the dive resorts have beaches also. All of them also have shore dives. I can name the resorts with beaches on one hand though. I'm talking about actual beaches where you can enter the water without a ladder - not Buddy's and similar. Eden Beach, Harbour Village, the Plaza, the Divi Flamingo, a couple of the south condo complexes - I don't think I've missed any. Everything else is on ironshore.
Predominantly these are at Klein Bonaire so require a boat/water taxi for access. However you can't take dive gear on the water taxi. One dive there we had two snorkelers on the boat - the mooring was only in about 20' and they swam towards shore.
Caribbean Snorkeling Sites | Bonaire Snorkeling Sites - Snorkel Sites
One other point to consider is that outside of the in town resorts there is absolutely
no facilities at any of the Bonaire dive sites. Except where the snack bus is currently working/making lunch. Many don't have much shade either.
To do both well, consider Curacao instead. Almost as many dive sites - but the vast majority of them are off public beaches. Same calm conditions. On Bonaire you're generally entering the water over ironshore/coral rubble. On Curacao the diving part of the reef is slightly farther out so you're typically entering via a sandy beach.
If your wife liked Grace Bay or Seven Mile Beach she'll be disappointed on Bonaire. I've been to both.
Many also have decent snorkeling or better. example: the north side of Playa Jeremi was written up in Frommers as one of the 10 best snorkels in the Caribbean once. It's also a good dive. One of few sites that
doesn't have facilities on-site. The Tugboat - one of the signature dives - is 17' deep. 100's of snorkelers go there from the cruise excursions. The dive part is better around the point on the deeper wall. There's a shop there and they have tables/refreshments. Not the best of the beaches.
At Varsenbaai while you're diving, your wife could be on the beach, snorkeling with the turtles in 6' of water south of it, or relaxing at the restaurant. Many of the Curacao sites have an on-site beach toy operator, an on-site dive operator, often a snack shop or small restaurant and the all important bathrooms. Porto Mari is a locals beach. It also has a double fringing reef an easy kick out.
You will drive farther between dive sites on Curacao since most are off the main road that bisects the island - requiring a typical 5-15min. drive to the water. On Bonaire - esp. the south side - the dive sites run basically back to back. And your resort is no more than 15mins. from anywhere. To completely drive across Curacao takes about an hour.
Klein Curacao is an uninhabited island, nice beach and probably a better snorkel than dive. Snorkel boats go out there on all day trips.
Curacao Travel- Caribbean, Curacao, Dutch Caribbean has more info. Curacao should be typically slightly cheaper and much easier to get to also. Accommodations on either island are about the same. Bonaire has more dive resorts - Curacao more resorts/hotels with on-site dive operations. Curacao has more non-dive things to do, famous shopping district downtown, nightlife, beach bars, casinos etc. Jazz is popular.
To get a good idea of the difference compare the site/entry photos for both here:
Scuba Shore Diving Region: ABC Islands
I do agree with the others about snorkeling on Bonaire. At Bari Reef after the dive I snorkeled around the old dock rubble for about an hour. Probably saw as much in 6' of water as I did down the reef. Many of the south sites drop off pretty gradually initially. And you can snorkel around the Salt Pier - the first sets of pilings can't be more than 20' or so deep. It's also a good dive.
