All investments are in essence dead money apart from for the recipient of it at a later date. The British ISA was actually a decent idea if you want to put money into UK businesses, but not at the detriment of other ISA products.
Getting money into the economy from savings is as much about giving people confidence to do it and not being worried about future shocks like energy prices, sudden changes in taxation and job security. I know people who are reasonably well off holding a lot of cash at the moment as they are really worried about job security. Most are well remunerated in PAYE roles. Yes people can say, that must be nice to earn enough to build a decent cash buffer, but they are only doing it as they can see how bad the jobs market is even for highly skilled people in the private sector.
For older people as they age they generally become much more risk averse and thats partly due to physical changes in the brain, but also not being able to work or gain employment due to ageism.
I've said it before, but the death of the final salary pension in the private sector was one of the worst things to happen and unfortunately it was Gordon Brown who put the final nail in the coffin back in 97. Its not only made everyone have to suddenly become financially astute investors, with no training, but also removed the security in old age. Annuities fail to offer decent income levels for a joint life policy under the conditions which the government is striving for, i.e. lower gilt yields and low inflation. Yes they have been good whilst interest rates were high but that is not great for the UK as a whole. This results in people not spending down their pension pots for fear of running out.
If we want people to get money into the economy, its much better to incentivise the desired behaviour in the first instance. Forcing people to do something almost always results in people trying to circumvent the system and secondary effects such as people being worried about future tax creep and hence stopping using pensions.
For the record I appreciate you are only trying to think of some potential solutions to a very difficult to solve problem.