The issue you have is the figures you are quoting are a look...

The issue you have is the figures you are quoting are a look back at dividend yield and are not necessary what is going to happen moving forward. Companies dont always pay out dividends and if you are relying on this as a source of income this in financial planners mind would be a risk and it is better having investments in long term government bonds etc. Yes they've performed crap like the rest of the market but they are a safer source of income than companies that can chose to pay out or not. Companies like PL8 warn about dividend yield traps. The value payout inferred may be high but the company may be performing poorly and your capital is being destroyed. Magellen, AGL and for some time AMP were examples of such traps. Holding a LIC like PL8 will take the guess work out of managing what each company is doing on a yearly/qtry/monthly basis but I wouldn't be putting all my eggs into this one basket and I'd diversify my investments.
PL8 hold 100% of its dollars in the Plato Australian Shares Income Fund which is a managed investment fund. So instead of waiting for quarterly distribution like a managed fund the LIC holds the fund collects the qtrly distributions and then spreads them out to investors on a monthly basis. This fund publishes monthly updates that list what AUM they have. Plato-Australian-Shares-Income-Fund-Prior-Monthly-Report.pdf In this case the fund has . ASSET UNDERMANAGEMENT of $2,453 MILLION
So when you look at a ETF like VAS it pays qtry distributions in most cases and this distribution should be added to your evaluation of how well you investment has performed. For the 12 months ending 30 June 2022, VAS paid out $6.26 in distributions per unit. For the 12 months to 30 June 2021, it was $2.33 per unit. The 12 months to June 30 2020 saw a total of $2.67 per unit. For the 12 months to 30 June 2019, it was a sum of $3.58 per unit. The 12 months to 30 June 2018 had VAS pay out $3.37 in distributions per unit. Currently it has paid out $2.77 per unit with one remaining distribution at the end of this month. just need to be careful as an investment now will see some capital gains the fund holds be passed on through to you when that distribution is paid so be wise if investing around the end of FY if you want to preserve capital and hold off to the new FY when the price should drop by the distribution value all things being equal. Your concern about buying in at highs is alleviated if you are dollar cost averaging into a stock over the long term Read the following articles about timing the market versus being out of the market etc. They are useful and show how waiting can cost you $ in the long run.

Counting the cost of timing the market | Vanguard Australia Personal Investor
How pausing contributions can add up | Vanguard Australia Personal Investor
Charting bear and bull markets | Vanguard Australia Personal Investor
What an Australian bias can cost a portfolio | Vanguard Australia Personal Investor.
The power of dollar-cost averaging | Vanguard Australia Personal Investor

I would say Nov-Dec for PL8 to so a SPP if it does one this year but that will all depend on markets at that time which is scary to predict at the moment and major events seem to always fall around Sept/Oct/Nov for markets.

again not financial advice and you must do your own research and make your own decision depending on what your personal circumstances are including risk appetite.