Is the [Coin-age] = [blocksize] * [age] ? Well i don't know too much about coding, but could you add a line like: IF [PoS-block-reward] < 0.1 AND [Coin-age] < 200 THEN [PoS-block-reward]=[PoS-block-reward]*4
This might not be exactly right, but if a 100 XMG block stakes in under two days it would get a higher reward.
Increasing the block reward for small blocks will definitely encourage big holders to divide their coins into small pieces. I think that this will be a good thing for the long term. Suppose someone has 10,000 XMG and divide it into 100 XMG blocks to maximize stake earnings. They find a PoS block and get a 0.1 XMG reward, instead of the 0.025 XMG reward that they would currently get. The amount of their total coins that staked is 1%. After the PoS block matures, to go on and sell their total balance of 10,000.1 they would have to spend the weight of the 99% of their coins that have not yet staked. The extra 0.075 XMG reward from the single block is actually less of a total reward then what would be earned if all 10,000 XMG staked all at once at the lower rate. I think that smaller blocks getting a higher reward will therefore discourage dumping, because it creates an opportunity cost of lost PoS reward for selling coins with a higher coin-age.
The main issue I see with this sort of change is that while it would create an incentive to split up large stacks of coins, it would also negatively impact the earnings of someone who was not technically-minded enough to try to get the most return out of the system.
In my opinion, a successful currency is a currency that works the same, no matter how much of it you have. A dollar is a dollar and a cent is a cent and, as such, the interest gained on a dollar and the interest gained on a cent are the same. If someone were to tell me that I could get a significantly higher interest rate by having less USD in my bank account, I would likely switch banks. The effort of maintaining many small accounts for increased returns might be worth my time, but it would significantly impact the ease-of-use of such a bank. Getting back to Magi, if a person new to the coin decided to invest heavily without reading up on the "interest tiers", they would probably not be too happy to discover their mistake later on.
If investing heavily and keeping coins in a neat stack or two can negatively impact the layman, I don't think a change like this is a good idea.
same as POW diff spike and the adjust reward delay can be abused by miners
any kind of POS that allow to have better results by micromanage will have people abuse this
in my opinion thats the wrong path to reward abuser or lets say min/maxer
the path u should go is to avoid any
fancy mine with full power when rewards are high and dont care about diff
and stop mining once reward adjustment did kick in taktiks
or place ur coins in some pattern for max POS results
it should be as simple as just POW mine
or just enable POS minting mode
and u have no disadvantage
for pos easy path is minimum size on coin pile for split stake happens guess for ur coin amount like 200 XMG would fit
and make sure that reduce of POS rewards wont kick in in a average 24/7 open wallet that have lot 200 XMG pile
u dont want to hurt 24/7 minter u want to make sure people who minte once any few months wasted POS rewards for not active support network as a node
regarding POW some interesting paths in discussion already with wolf u have a gpu mining pro who can help ya customize a algo solution that even if GPU mineable it wont outperform CPU in area hashrate/watt
also i strong belive in mobile wallets as a solution for the future
mobile wallet that is able to stake and even mine when loading over night would be ideal solution
storage on mobile devices will grow blockchain size as issue will be less and less each year
I met someone a few days ago on bleutrade that is a miner and trader of magi. He has 750kh/sec on supernova and mines around 150 XMG per day. He has 7000 XMG in an offline wallet that he doesn't even bother staking because the incentive isn't worth it, and he keeps most of his coins on exchanges. His profits on magi: PoS < PoW < Catching dumps and placing higher sell orders. He claimed to make more than 150 XMG per day just on market volatility. 
Additionally, PoW mining seems to cause more issues with block chain forks than PoS in my experience.