I visited the Musée de l'Air at the beginning of February. An aviation career fair happened to be running on the day I'd set aside, so admission to the museum and the aircraft was free!
As on my prior visit, I took the RER, got off au Bourget (in French, "at" and the masculine form of "the" combine: à + le = au) and walked. Normal safety rules apply, but my mid-morning and mid-afternoon non-Roissy-express trains were filled with ordinary working people doing errands. I had visited the Mémorial de la Shoah at Drancy a few days before, so I felt quite comfortable walking around Le Bourget.
In fact, a current Musée de l'Air exhibit, La Légende des Cieux, requires walking. It's a series of 21 portraits of aviation heroes, painted on walls around town. It runs only until September, but maybe the outdoor format will be reprised in the future.
If you walk, the Centre Culturel André Malraux is half a block up from Le Bourget station. When I was there, there was a photography exhibit, part of a digital arts festival for the Île de France region. The staff member at the desk was welcoming, free snacks and drinks were offered, and there was a clean restroom.
On the main street, the Hôtel de Ville du Bourget ("of" and masculine "the" combine; de + le = du) is an impressive red brick tower with beautiful metal sign work. Farther along, you can see Franco-Prussian War bullet holes in the vestibule of the Église Saint-Nicolas, and your husband might enjoy the aviation-themed side altar, framed by wooden propeller blades!
If you take the bus, there's no need to go to all the way to Roissy for the 350. The 148 and 152 both run from closer RER stations (and from suburban Métro stations if you don't mind a long ride) to the Musée de l'Air. RATP's "Next Stop Paris" app has maps and schedules.
I love the Musée de l'Air. It's rarely busy, and being inside Le Bourget's grand old passenger terminal or out on the desolate tarmac adds to the sense of nostalgia. The permanent exhibits are a bit worn, to be honest. There's a fearsome, moth-eaten flight attendant mannequin at the back of one of the Concordes, and the audio recording in the Caravelle cockpit exhibit is dead.
Still, walking through the retired Air France 747, whose walls, ceiling, and floor have been cut away in places, makes you realize that when you fly, you are in little more than an aluminum can. You can knock on the inside of the fuselage to appreciate how thin the metal is.
The nuclear missile cut-away in the basement of one of the hangars is fascinating (and scary to contemplate). I don't know that there's any other place in the world where one can see such a thing up close.
I didn't attend a planetarium show this time, but I remember remarking that the narrator had held my attention and done a good job explaining what we were looking at, when I went in 2009.
There are other paid add-ons such as a flight simulator, but the numerous and detailed signs (in French only) outlining the limitations of these interactive exhibits give me the impression that patrons have been disappointed.
The gift shop has declined and is now full of commercial kitsch. At least the books are still interesting!