A couple of points to consider -

1. Maximizing your AA miles will be easier if you do the bulk of the trip as a Platinum member rather than a Gold, as you'll earn a 100% mileage bonus on flights with AA, CX, QF and AY flight numbers (also IB, RJ and LA.) You don't earn this bonus on JL, MA and BA-designated flights. You can earn it on AA codeshares on BA or JL flights when you're connecting to/from an AA flight.

2. Irrespective of the current (expiring) 10% discount on xONEx fares, the price of a DONE4 begun in certain European countries is up to US$2000 cheaper than in the US (of course depending on exchange rates.) As of now, for example, DONE4s begun in Sweden, Poland, Jordan or Israel are anywhere from $1800 - $2100 cheaper than ex-USA. Those savings could easily cover the cost of an access trip before and/or after (or you could use miles and pocket the difference in cash.) Because of the current Dollar:Sterling exchange, even DONE4s begun and ended in the UK are $1500 cheaper than in the US (which is a stunning reversal of the situation from just a year or two ago.)

3. There are pros and cons to this approach; obviously it's less convenient, and the rule about stopovers in the continent of origin reduces your freedom of movement (in Europe - but expands it in N. America.) However, you could combine your access trip to Europe to hit a couple of your "musts" en route, e.g. FCO or BUD, and free up segments for use elsewhere, in particular N. America and Oz/NZ, where not only are the segments longer, but the double mileage bonus is always in force. In general an xONEx is not the most cost-effective way of doing short-haul trips around Europe.

So my recommendation would be to originate in Europe after hitting a couple of your "musts." Sign up for the Plat Challenge (see the AA board if unfamiliar with this) before you leave the US and use your access trip and the RTW itself to confirm your Plat status, then let your Plat status leverage a lot of extra miles. Depending on your route, you could leverage an extra 30,000 redeemable miles off a 45,000-mile RTW itinerary (around 90K mi vs. 60K as an AA Gold member.)

Edited to add - if you don't need to return to N. America en route, you could earn a lot more miles by originating in Europe and substituting South America for North America, using an itinerary that goes Europe > S. America > Oz > Asia > Europe. There are lots of great longhaul segments possible in S. America, and Lan's service is simply excellent. The Plat challenge would be an issue (only EQP earned on AA metal or codeshares counts) but you could do it in a mileage run or two prior to leaving the US for your access trip.