The Taiwanese variant of the M113 has gone through at least 5 upgrade phases, new armor and new engines not to mention new armaments. But what I'm trying to point out is that could be upgraded to something thats close enough to a Bradley just without the missile launchers. Its not expensive and will save money compared to buying new APCs.
It really depends on how sound the hulls are; for all we know, the M113's could be on their last legs due to metal fatigue and hull cracking. I've seen plenty of Leopard I's that otherwise look OK on the outside been put out to pasture as gate guardians because of metal fatigue and hull cracking.
What has to be done is a complete survey on the condition of the M113 fleet. That means the hulls need to be jacked up and completely ultra-sounded to determine the hull thickness and to find any cracks in the hull. After that, they have to decide how to move forward. If the hulls are in pretty bad shape, there is no point in modernizing them again as it is a waste. Better off building or buying a new APC if the hulls are in bad shape.