I don't think is nice encouraging someone to invest on Bitcoin using his 30% of salary to invest on Bitcoin because there is every possibility that the investor could ran into trouble if the reserve fund is not enough to sustain him till he receives his next salary, so perhaps in as much as is advisable to take advantage of the Bitcoin price right now but shouldn't get overwhelmed by investing aggressively because is better to invest with the money we can easily afford without being tampered than investing with all the money we have and within a short while you end up selling it do to the lact of money to take care of other needs, however is only those that have structured one of there portfolio for Lump suming I could easily advise to take advantage of the market because they have already taken all the measures before now.
There is no fixed percentage that is universal as regarding what to invest in Bitcoin. It is always to each his own; you are expected to work out what you will be comfortable to leave in Bitcoin, an amount that will not stop you from living your normal life. There are some people people whose 10% of their income is enough for their needs and they will still have surplus from it. Those are the people at the upper echelon of society that are making decent amount of money that are way above what they can possibly spend. This set of people can even afford to invest 50% of their income into Bitcoin.
If I fall into this category of people, I will definitely put at least 50% of my income into Bitcoin because I don't know of any better asset class to invest in and save for retirement. My plan is to build a good portfolio that I will pass on to heirs, so saving my funds in Bitcoin is similar to the retirement savings and generational wealth preservation.
In another dimension, there are people whose income are so low that it will take over 50% to as high as 70% of their income to meet their basic needs. These class of people can invest as low as 10% of their income and they will not be breaking any rule. It is always ideal to properly calculate your cashflow to be able properly know what to put into Bitcoin to be able to have the much needed peace for long term investment.