Performing Buddha Puja even after the Buddha has entered Parinibbana can give immeasurable results.
This is what I found in the texts.
Sudhāpiṇḍiya Theraapadana
Pūjārahe pūjayato,
buddhe yadi va sāvake;
Papañcasamatikkante,
tiṇṇasokapariddave.For one who worships those worthy of worship —
whether Buddhas or disciples —
who have gone beyond proliferation,
who have crossed sorrow and lamentation —Te tādise pūjayato,
nibbute akutobhaye;
Na sakkā puññaṁ saṅkhātuṁ,
imettamapi kenaci.For one who worships such ones,
peaceful and fearless —
the merit cannot be measured,
not even this much by anyone.Catunnamapi dīpānaṁ,
issaraṁ yodha kāraye;
Ekissā pūjanāyetaṁ,
kalaṁ nāgghati soḷasiṁ.Even if one were ruler
of the four continents —
that would not equal
one sixteenth part of a single act of worship.Commentary:
Pūjārahā nāma buddhapaccekabuddhaariyasāvakācariyupajjhāyamātāpitugaruādayo.“Worthy of worship” means:
Buddhas, Paccekabuddhas, noble disciples, teachers, preceptors, parents, and other venerable persons.“Papañcasamatikkante” = those who have gone beyond mental proliferation (craving, conceit, views).
“Tiṇṇasokapariddave” = those who have crossed sorrow and lamentationTesu pūjārahesu mālādipadumavatthābharaṇacatupaccayādīhi pūjayato…
puññakoṭṭhāsaṁ sahassasatasahassādivasena saṅkhyaṁ kātuṁ kenaci mahānubhāvenāpi na sakkā.If one worships such worthy ones with garlands, flowers, cloth, ornaments, or the four requisites, the amount of merit cannot be calculated — even by a being of great power.
Even after the Buddha’s Parinibbāna, worship of relic shrines, images, or Bodhi trees produces immeasurable merit.
Catunnamapi dīpānaṁ… jambudīpa-aparagoyāna-uttarakuru-pubbavidehānaṁ…
sakalacakkavāḷagabbhe issaraṁ cakkavattirajjaṁ kareyya.Ekissā pūjanāya etaṁ… soḷasakkhattuṁ vibhattassa soḷasamakoṭṭhāsassa na agghati.
Even ruling over the four great continents —
Jambudīpa, Aparagoyāna, Uttarakuru, and Pubbavideha —
with all their minor islands,
as a Universal Monarch —would not equal one-sixteenth of the merit of a single offering made at a relic shrine.
The commentary on the Apadāna of Venerable Tipupphiya also shows the results of worshiping a shrine (in this case it is a Bodhi Tree).
Beginning with “Migaluddo pure āsiṃ…,” this is the Apadāna of the venerable Tipupphiya.
In a former life, due to an unwholesome act, he was born into a hunter’s family in the time of the Buddha Vipassī. Living in the forest as a deer-hunter, he once saw the Pāṭali Bodhi tree, full with leaves and green-blue in color. He worshipped it with three flowers and bowed as if before the Buddha himself.
Through that merit he was reborn in heaven and enjoyed divine prosperity. Later, as a human, he enjoyed the prosperity of a Universal Monarch. In this Buddha’s dispensation he was born in a family, gained faith upon hearing the Dhamma, went forth, and soon attained arahantship.
Verse 31 explains: “I was formerly a deer-hunter.” A deer is so called because it is pursued or seeks food; a hunter is one greedy for killing deer. Seeing the green Pāṭali tree, red in blossom but green in leaves, he worshipped it.
The rest is clear.
Thus ends the commentary on the Apadāna of Tipupphiya Thera.
Migaluddo pure āsintiādikaṃ āyasmato tipupphiyattherassa apadānaṃ. Ayampi purimabuddhesu katādhikāro antarā kenaci akusalacchiddena vipassissa bhagavato kāle nesādakule nibbatto migaluddo hutvā araññe viharati. Tadā vipassissa bhagavato pāṭalibodhiṃ sampuṇṇapattapallavaṃ haritavaṇṇaṃ nīlobhāsaṃ manoramaṃ disvā tīhi pupphehi pūjetvā purāṇapattaṃ chaḍḍetvā bhagavato sammukhā viya pāṭalimahābodhiṃ vandi. So tena puññena tato cuto devaloke uppanno tattha dibbasampattiṃ aparāparaṃ anubhavitvā tato cuto manussesu jāto tattha cakkavattisampattiādayo anubhavitvā imasmiṃ buddhuppāde ekasmiṃ kulagehe nibbatto vuddhimanvāya satthu dhammadesanaṃ sutvā paṭiladdhasomanassahadayo gehaṃ pahāya pabbajitvā nacirasseva arahā ahosi. 31. So evaṃ siddhippatto attano pubbakammaṃ saritvā somanassajāto pubbacaritāpadānaṃ pakāsento migaluddo pure āsintiādimāha. Tattha maraṇāya gacchati pāpuṇātīti migo, atha vā magayamāno ihati pavattatīti migo, migānaṃ māraṇe luddo lobhī gedhoti migaluddo, pure mayhaṃ puññakaraṇasamaye kānanasaṅkhāte mahāaraññe migaluddo āsinti sambandho. Pāṭaliṃ haritaṃ disvāti tattha pakārena talena rattavaṇṇena bhavatīti pāṭali , pupphānaṃ rattavaṇṇatāya pāṭalīti vohāro, pattānaṃ haritatāya haritaṃ nīlavaṇṇaṃ pāṭalibodhiṃ disvāti attho. Sesaṃ sabbattha uttānatthamevāti. Tipupphiyattheraapadānavaṇṇanā samattā.