Ecclesiastes 9:1 For all this I considered in my heart even to declare all this, that the righteous, and the wise, and their works, [are] in the hand of God: no man knoweth either love or hatred [by] all [that is] before them.
[2] All [things come] alike to all: [there is] one event to the righteous, and to the wicked; to the good and to the clean, and to the unclean; to him that sacrificeth, and to him that sacrificeth not: as [is] the good, so [is] the sinner; [and] he that sweareth, as [he] that feareth an oath.
[3] This [is] an evil among all [things] that are done under the sun, that [there is] one event unto all: yea, also the heart of the sons of men is full of evil, and madness [is] in their heart while they live, and after that [they go] to the dead.
[4] For to him that is joined to all the living there is hope: for a living dog is better than a dead lion.
[5] For the living know that they shall die: but the dead know not any thing, neither have they any more a reward; for the memory of them is forgotten.
[6] Also their love, and their hatred, and their envy, is now perished; neither have they any more a portion for ever in any [thing] that is done under the sun.
You'll note that this entire discussion is premised on the fact that it matters not whether you are evil or righteous, the same fate befalls all men. Period. The place of existance after death therefore is of no consequence. Physical life and Spiritual life are two seperate things just as spiritual death and physical death are two seperate things. This passage is telling us that regardless of Spiritual considerations, upon physical death we have nothing more to do with anything that happens under the sun. IE, the dead grandmother cannot dwell on earth, affect anything on earth, hear, see or smell anything on earth, ect. because it is forbidden.
Now, noting that, it makes all your philosophy and reasoning about praying to the dead - moot.. about praying to Mary - moot. About praying to other saints - moot. There are countless scriptures that forbid it on it's face to begin with; but, this passage states there is nothing to be gained from even attempting it because there can be no interaction between us and those who have gone before us.
Chapter 8 sets this up with a discussion of all that is done while men are yet physically alive and the rammifications of their living pursuits. There is no place to interject any assumptions about spiritual life or death into this. That is dealt with and passed over by saying all things happen to both and the common fate is included - physical death which includes an inability to interact further with the physically living - period. QED.