OK - let's try something "off the wall". Caligula was not mad, just misunderstood!!
It was Constantine whom history records as first seeing that the empire could not be ruled from Rome, but that the centre of government needed to be more to the east. That was where the grain supply for the west came from, and where the most real and organised threat, Parthia, lay.
But actually, if one prises back the Augustan myth, one can glimpse something of the same in the thinking of Antony and Cleopatra before Actium - an eastern empire ruled from Alexandria; and a dynasty of quasi-godlike beings. this, to me, was the actuality behind the so-called and controversial "Donations of Alexandria".
Now Gaius Caligula was a direct descendent of Antony - Antonia (Gaius' grandmother) was Antony's daughter. Is it possible that the Antonian "dream" or vision of empire descended to Gaius?
I see a good deal of method also in Caligula's assuming absolute powers as Caesar - perhaps seeking to move the principiate towards an Empire in terms understood in the east. He had seen Tiberius attempts to shrink from the full titulatur and powers of the monarchy; to rule with the Senate. He had seen Augustus' hidden empire and new it as a sham.
As a young man with the prospect of many years of rule ahead of him, Caligula may have determined to set what to him might have seemed a more honest, workable, pragmatic, and potentially successful course. He was the first Princeps to grow up under the principiate and to know nothing else - don't forget Tiberius' father had been a republican. His vision may have been different - as Antony's was different from Octavian's.
It also seems that Gaius had a keen sense of humour - perhaps ironic, perhaps sarcastic or punning. I think the Cincinnatus as Consul story/and perhaps the huts/seashells one too, were misread or distorted examples of jokes.
As for the invasion of Britain, Claudius too was faced with mutiny. Gaius may have had to put a brave face on a similar circumstance.
As for the manoeuvres in Germany which Tacitus (? or was it Suetonius?) ridicules. They sound to me like getting an army into shape and perhaps punishing some units who had not been up to scratch. Practical not laughable, in other words.
Did Caligula have an illness which changed him? Maybe? Did he have incest with his sisters? Again maybe - Agrippina the Younger was no saint it seems - but maybe it was political propaganda. the remaining children of Germanicus had suffered a few years that must have been frightening under Sejanus - the elder brothers imprisoned and killed; their mother exiled. Were they just close?
And brother-sister marriages were a norm in Egypt even under the Macedonian/Greek-born Ptolomies. So back to the Antonian dream. It can be argued that he and Cleopatra intended to marry Caesar's son, Caesarion, to their own child Cleopatra Selene. Was Caligula thinking of a similar approach for the future of the Julio-Claudian's? Was it so far fetched? Look at the way Augustus inter-married his relations - Julia to Agrippa; Agrippina the elder to Germanicus (who's step-grandmother was Augustus' sister Octavia. Was not this keeping it "in the family"?
So, as with Richard III, Caligula will probably never lose the evil legend that attaches to his name. But i do think other interpretations are possible.
Phil