Without knowing your mode of travel, it is difficult to say anything substantial, except that I would think that any travel to Romania would try to include Maramures and/or Bucovina.

http://www.flickr.com/photos/mksfca/4186107194/in/set-72157623001926246/

http://www.flickr.com/photos/mksfca/4186116056/in/set-72157623001926246/

I'm mainly going by trains, buses, and some free flights. Nice pictures by the way. 35mm?

Back then, I used a 35 mm SLR.

Budapest - 6 nights
Cluj Napoca - 2 nights
Brasov - 2 nights
Sibiu - 2 nights
Bucharest - 3 nights

I think Buda is too long for 8 nights, Brasov and Sibiu 2 nights imore than enough. Bucharest 3 will do it and you may be pulling your hair out by then

Plojesti might be worth a couple of nights, if you are going in winter there are some ski resorts around there which are good value

To comment on the Romanian part of your itinerary, 2 nights is enough for Cluj and Bucharest each, as well as for Sibiu if you don't do any side trips.

But leave 3-4 nights for Brasov - apart from visiting the city you definitely should do some day trips to the many sites around it: the former royal palace Peles in Sinaia (one hour by train), the medieval citadel Sighisoara (two hours by train; you could also spend one night there), the fortress in Rasnov (20 minutes by bus or train ), the old fortified churches in Harman and Prejmer (20-30 minutes by bus or train), even the famous fake Dracula's castle in Bran (40 minutes by bus).
You could also use it as a base for the ski resorts on the upper Prahova Valley that I think Bilboburgler is referring to (they are much closer to Brasov than to Ploiesti).

As note on transports don't use trains between Brasov-Sibiu and Sibiu-Bucharest (the railways on these routes are closed or indirect so buses are much faster).
On the way from Sibiu to Bucharest you could make a brief stop to visit the 14th century Cozia monastery (it's about one hour and half south of Sibiu).