*wikis up genealogy* Well, succession in Bavaria is secured, due to Joseph Ferdinand's half-brothers... but they are just haöf-brothers and have no claim to the Spanish throne. So indeed it would again be a fight between Habsburgs and Bourbons. Just that this time (1730-1740), Habsburg has been reduced to Emperor Charles VI. Unlike 30 years earluer IOTL, the Habsburgs could not produce a junior member to start an own branch in Spain (that was Charles initial role...), as Charles VI is the last remaining male Habsburg. Though, as both his daughter were married with Lorraines (and thus both would form the combined house of Habsburg-Lorraine) I guess he could present his younger daughter Maria Anna and her husband, Charles Alexander of Lorraine as candidates for the Spanish throne....
And by, say, 1735 (being in the exact middle of 1730 and 1740) Spain is not that overpowerful compared to the rest of Europe anymore as it was in 1701. Interstingly enough, in 1735 there already IS a succession war going on, the one of the Polish Succession. And 5 years later there will be a War of the Austrian Succession! Really, one doesnt even need to
try to make a succession-wank in this time period

But this also makes the sides clear: Saxony will back Austria, as France is the enemy in Poland, while Bavaria will back France as IOTL, as it has its own claims for the Austrian succession. Prussia will remain neutral, as it generally did unde rteh Soldier King Frederick William, whereas most other HRE states will back Austria as they did in most wars against France IOTL...