My husband (73) and I (66) had a wonderful trip planned for this past December. ...until he fell and broke his leg on Thanksgiving night. Trip off. I am now (after sufficient time to pout) going to rebook it but thought I would run through my proposed itinerary to get comments and see if I should amend any segment, length of time or lodging from previous itinerary. We are experienced travelers with interests in the local culture. Meandering is a favorite activity in a new city, besides the "must see" places.
5 days Buenos Aires -Duque Boutique Hotel in/near Palermo Soho
am flight , Lan, to Iguazu Falls, Ar - arrive noonish, 2 nts Hotel das Cataratas
pm flight, Tam, to Salvador de Bahia, 4 or 5 day? Casa do Amarelindo
Tam flt, Salvador to Rio, 3, 4, or 5 days including New Year's Eve, day
love to stay at Ipanema Beach but prices outrageous at this time - (don't want to pay
more than $400/nt
previous booking was at O Veleiero B & B up in the hills.
Also, any thoughts on discount airlines or booking engines?

despegar.com
argentinaforless.com

Looks fine...

Good. What do the other experts have to say?

When exactly are you going? (Carnaval is coming up soon; prices rise and availability is effected. but it is a very lively time.)
In Rio, the longer the stay, the better time you'll have, but it will be very hot/humid for sightseeing. Try the Praia Ipanema (or give a price range for better advice). The bondinho up to Santa Teresa is still not working, so don't consider staying up there right now (but do visit to see the views and the architecture. Lunch at Aprazivel). Good info site is www.ipanema.com
More time in Salvador gives you more time to do day or overnight trips to some nearby places like Morro do Sao Paulo, Itaparica, Guarajuaba, Cachoeira, etc. Good info site is www.bahia-online.net

Also in Salvador, there is now a hop-on/hop-off bus that goes to all the sights, including some further out. Seems a good deal for someone with a recent physical problem.