AA has never given me a problem upgrading on the any fare including the 'netsaver' (N/L fares). I booked in Feb to fly in Nov for $196 to LHR from DFW via JFK and request upgrade to biz and got them right away. Flight from DFW to JFK was in F and then biz to LHR. Got to use the arrivals lounge at LHR (shower/breakfast) and the use of Admirals clubs at DFW, JFK and LHR even though I'm not a member. You can use the Admirals clubs flying biz or F on international flights. Even got coupons for free drinks.
Booked a MR to ATL in Dec for flights on Jan 1 and got F class also. Breakfast going and Dinner returning all for $159 netsaver fare and DOUBLE miles promotion.