I have a different take on the weight issue.
The advantages of the 60 series flashes are:
1) Power; and
2) Recycling time; and
3) Location of the weight.
The 45 series flashes have the batteries in the handle, while the 60 series flashes move the battery into a shoulder pack, thus splitting the weight. In total, the weight of the 60 series handle and power pack is greater, but if you attach the handle to the camera using a bracket, the handle plus bracket of the 60 series flash weighs less than the 45 series handle plus bracket.
For many years I used a Metz 202 and 402 combination. I then went to a Metz 60CT2. The 60CT2 gives me TTl with my Olympus OM2. Recently, I've added a 60CT1. I think the 60CT series units are great, and prefer them to the 45 series flashes.
With respect to the batteries, they are quite resilient. It isn't good to leave them unused for a long time, but you might be surprised.
The batteries are quite expensive ($70.00 US), but in my experience they last for a long time. There used to be a number of alternate sources (the batteries themselves are used in other types of equipment, with just minor (almost cosmetic) modifications), but I must confess I haven't seen them recently.
Matt